Blood Test Biomarkers Guide: 15,000+ Markers | Kantesti AI

Also known as: Erythrocytes, Red Cell Count

Red blood cells carry oxygen from lungs to tissues and return carbon dioxide for exhalation. Each RBC contains hemoglobin, the iron-rich protein that binds oxygen molecules. RBC production occurs in bone marrow and is regulated by erythropoietin hormone from the kidneys.

Also known as: Haemoglobin

Hemoglobin is the iron-containing protein within red blood cells that transports oxygen throughout the body. Each hemoglobin molecule contains four heme groups, each binding one oxygen molecule. Also helps transport CO2 and maintain blood pH.

Also known as: Packed Cell Volume (PCV), Crit

Hematocrit represents the percentage of blood volume occupied by red blood cells. It provides quick assessment of blood's oxygen-carrying capacity and fluid balance.

Also known as: Mean Cell Volume, Average RBC Size, high mcv blood test meaning

MCV measures the average size of red blood cells in femtoliters. This critical index helps classify anemias into microcytic (MCV<80), normocytic (80-100), and macrocytic (>100). Essential for determining the underlying cause of anemia and guiding treatment.

Also known as: Mean Cell Hemoglobin, Average Hemoglobin per RBC

MCH quantifies the average amount of hemoglobin contained in a single red blood cell, measured in picograms. This index reflects both cell size and hemoglobin content. MCH typically correlates closely with MCV—larger cells contain more hemoglobin.

Also known as: MCHC bajo en sangre que significa, Hemoglobin Concentration

MCHC represents the average concentration of hemoglobin within red blood cells. Unlike MCH which measures total hemoglobin per cell, MCHC reflects hemoglobin density. This marker remains relatively stable and helps identify spherocytosis when elevated or hypochromic conditions when decreased.

Also known as: RDW-CV, RDW-SD, RDW en sangre, rdw blood test, what is rdw in blood test, rdw cv blood test high

RDW measures the variation in size (anisocytosis) among red blood cells. RDW-CV (coefficient of variation) is expressed as percentage, while RDW-SD (standard deviation) is measured in femtoliters. High RDW indicates significant variation in cell sizes, often seen in nutritional deficiencies or mixed anemias.

Also known as: Leukocytes, Total WBC Count

White blood cells are the cornerstone of your immune system, defending against infections and abnormal cells. Total WBC includes five main types: neutrophils, lymphocytes, monocytes, eosinophils, and basophils—each with distinct immune functions.

Also known as: Neutrófilos altos, PMNs, Polys, antibiotics for high neutrophils

Neutrophils are the most abundant white blood cells, serving as first responders to bacterial infections. These phagocytic cells engulf and destroy bacteria through oxidative bursts. They have a short lifespan (8-12 hours) and are continuously produced at rates exceeding 100 billion cells daily.

Also known as: Lymphs, T-cells, B-cells, NK cells

Lymphocytes include T-cells (cell-mediated immunity), B-cells (antibody production), and Natural Killer cells. They provide targeted responses to specific pathogens and maintain immunological memory.

Also known as: Monos, Macrophage precursors

Monocytes are precursors to tissue macrophages. They phagocytose pathogens, present antigens, and orchestrate inflammatory responses, bridging innate and adaptive immunity.

Also known as: Eos, Eosinophil Count

Eosinophils combat parasitic infections and mediate allergic inflammatory responses. They contain cytotoxic proteins that damage parasites but can also cause tissue damage in allergic conditions.

Also known as: Basos, Basophil Count

Basophils are the least common circulating white blood cells. They contain histamine and heparin, contributing to allergic reactions and inflammation.

Also known as: Thrombocytes, Platelet Count

Platelets are small cell fragments essential for blood clotting and hemostasis. They aggregate at damaged blood vessel sites, form a platelet plug, and release factors that activate the coagulation cascade.

Also known as: mpv blood test normal range

MPV measures average platelet size, reflecting bone marrow platelet production activity. Larger platelets are younger, more metabolically active, and have greater thrombotic potential.

Also known as: normal reticulocyte count, Retic Count

Reticulocytes are immature red blood cells released from bone marrow. They reflect bone marrow's ability to respond to anemia and classify anemia as hypo-regenerative (low reticulocytes) or regenerative (high reticulocytes).

Also known as: SGPT, Alanine Transaminase, ALT SGPT

ALT is an enzyme found predominantly in liver cells (hepatocytes), making it highly specific for liver damage. When liver cells are injured, ALT leaks into the bloodstream. ALT is more liver-specific than AST and is the primary marker for hepatocellular injury, particularly useful in diagnosing and monitoring viral hepatitis, fatty liver disease, and drug-induced liver injury.

Also known as: SGOT, Aspartate Transaminase, AST Blood Test Definition

AST is an enzyme found in liver, heart, muscle, kidney, and brain tissues. Unlike ALT, elevated AST is less specific for liver disease and may indicate cardiac or skeletal muscle damage. AST exists in two forms: cytoplasmic (released with mild injury) and mitochondrial (released with severe cell damage). The AST/ALT ratio helps differentiate liver disease causes.

Also known as: Alk Phos, AP

ALP is found in liver (biliary epithelium), bone, intestine, kidney, and placenta. Elevated ALP indicates cholestatic (biliary) liver disease or bone disorders. ALP rises when bile flow is obstructed, making it a marker for biliary obstruction, primary biliary cholangitis, and infiltrative liver diseases. Bone ALP increases with increased bone turnover.

Also known as: Gamma GT, GGTP, Gamma G Transferase

GGT is a sensitive but non-specific marker of liver and biliary disease, found in liver, kidneys, pancreas, and intestines. It's particularly useful for confirming hepatic origin of elevated ALP and detecting alcohol-related liver damage. GGT is induced by alcohol and certain medications, making it a marker of alcohol use even without liver disease.

Also known as: TBIL, Serum Bilirubin

Bilirubin is the yellow breakdown product of heme from red blood cell destruction. The liver conjugates (makes water-soluble) bilirubin for excretion in bile. Total bilirubin includes unconjugated (indirect) and conjugated (direct) forms. Elevated bilirubin causes jaundice—yellowing of skin and eyes visible when levels exceed 2.5-3 mg/dL.

Also known as: Serum Albumin, ALB

Albumin is the most abundant plasma protein, synthesized exclusively by the liver. It maintains oncotic pressure (preventing fluid leakage from blood vessels), transports hormones, fatty acids, drugs, and bilirubin, and serves as a marker of liver synthetic function and nutritional status. Albumin has a half-life of ~20 days, so levels change slowly.

Also known as: TP, Serum Total Protein, Total Protein in Blood Test

Total protein measures all proteins in serum, primarily albumin (60%) and globulins (40%). Albumin is made by the liver, while globulins include immunoglobulins (antibodies) made by plasma cells and other proteins. Total protein reflects nutritional status, liver function, kidney function, and immune system activity. The albumin/globulin ratio provides additional diagnostic information.

Also known as: Serum Globulin, Alpha 1 Globulin, Alpha 2 Globulin, Low/High Globulin Levels

Globulins are a diverse group of proteins including alpha-1 globulins (alpha-1 antitrypsin, alpha-fetoprotein), alpha-2 globulins (haptoglobin, ceruloplasmin), beta globulins (transferrin, complement), and gamma globulins (immunoglobulins/antibodies). Serum protein electrophoresis (SPEP) separates these fractions for detailed analysis.

Also known as: CysC

Cystatin C is a small protein produced by all nucleated cells at a constant rate, freely filtered by glomeruli, and completely reabsorbed and catabolized by tubules. Unlike creatinine, cystatin C is independent of muscle mass, age, sex, and diet, making it more accurate for GFR estimation in elderly, malnourished, or muscular individuals.

Also known as: Serum Urate

Uric acid is the end product of purine metabolism in humans (we lack uricase enzyme). Purines come from dietary sources (red meat, seafood, beer) and cellular breakdown. Two-thirds of uric acid is excreted by kidneys; one-third by the gut. When uric acid exceeds its solubility (~6.8 mg/dL), monosodium urate crystals can precipitate in joints (gout) or kidneys (stones).

Also known as: UA Urobilinogen, Urobilinogen in Urine Test

Urobilinogen is produced when intestinal bacteria reduce bilirubin. Most is excreted in feces (as stercobilin, giving stool its brown color), but some is reabsorbed and excreted in urine. Urobilinogen in urine reflects bilirubin metabolism and enterohepatic circulation. High levels indicate increased bilirubin production or liver dysfunction; absent levels suggest bile duct obstruction.

Also known as: Thyrotropin

TSH is produced by the pituitary gland and regulates thyroid hormone production through negative feedback. It's the most sensitive screening test for thyroid dysfunction. When thyroid hormones drop, TSH rises (hypothyroidism); when thyroid hormones are excessive, TSH is suppressed (hyperthyroidism). TSH changes exponentially with small changes in free T4.

Also known as: FT4, Free Thyroxine

T4 (thyroxine) is the main hormone produced by the thyroid gland. About 99.97% is protein-bound; only 0.03% is "free" and biologically active. Free T4 is converted to T3 (the active hormone) in peripheral tissues. Measuring free T4 avoids interference from protein binding changes that affect total T4 (pregnancy, estrogen, liver disease).

Also known as: FT3

T3 is the biologically active thyroid hormone, 3-5 times more potent than T4. About 80% of T3 is produced by peripheral conversion of T4 by deiodinase enzymes; only 20% comes directly from the thyroid. T3 is essential for metabolism, heart rate, body temperature, and cognitive function. Free T3 represents the unbound, active fraction.

Also known as: Thyroid Peroxidase Antibodies, TPOAb, Anti-TPO

Anti-TPO antibodies target thyroid peroxidase, the enzyme essential for thyroid hormone synthesis. These autoantibodies are the most sensitive marker of autoimmune thyroid disease. They're found in over 90% of Hashimoto's thyroiditis and 70% of Graves' disease patients. Presence indicates autoimmune thyroid inflammation even when thyroid function is currently normal.

Also known as: Pro Time, INR

PT measures the extrinsic and common coagulation pathway function (factors I, II, V, VII, X). INR (International Normalized Ratio) standardizes PT results across laboratories using different reagents. PT/INR monitors warfarin therapy and assesses liver synthetic function. Vitamin K-dependent factors (II, VII, IX, X) are affected by warfarin and liver disease.

Also known as: PTT, aPTT Normal Range, High aPTT, aPTT Laboratory Test

aPTT measures the intrinsic and common coagulation pathway function (factors I, II, V, VIII, IX, X, XI, XII). It's used to monitor unfractionated heparin therapy and screen for bleeding disorders like hemophilia A (factor VIII deficiency) and hemophilia B (factor IX deficiency). aPTT is also prolonged by lupus anticoagulant (paradoxically increases clotting risk).

Also known as: Elevated D-Dimer Meaning, Fibrin Degradation Product

D-dimer is a fibrin degradation product formed when plasmin breaks down cross-linked fibrin in blood clots. Elevated D-dimer indicates recent or ongoing clot formation and breakdown. It's a highly sensitive but non-specific test for venous thromboembolism (VTE)—a negative D-dimer effectively rules out DVT and PE in low-risk patients.

Also known as: Factor I, Clotting Factor I

Fibrinogen is a glycoprotein synthesized by the liver and converted to fibrin by thrombin during clot formation. It's both a coagulation factor (essential for clot stability) and an acute phase reactant (rises with inflammation). Fibrinogen levels affect both bleeding risk (when low) and thrombotic risk (when elevated, as it promotes platelet aggregation and increases blood viscosity).

Also known as: hs-TnI, hs-TnT, Cardiac Troponin

Cardiac troponins are structural proteins in heart muscle released when cardiomyocytes are damaged. High-sensitivity troponin assays detect very low levels, enabling earlier MI detection but also detecting non-ischemic cardiac injury. Troponin is the gold standard for diagnosing myocardial infarction, with a rise and/or fall pattern with at least one value above the 99th percentile.

Also known as: Brain Natriuretic Peptide, What is a Dangerous BNP Level

BNP and NT-proBNP are released from ventricular myocytes in response to wall stretch and volume overload. They're the primary biomarkers for diagnosing and prognosticating heart failure. BNP has a shorter half-life (20 min) than NT-proBNP (120 min), so NT-proBNP levels are higher. Both correlate with heart failure severity and predict adverse outcomes.

Also known as: Creatine Kinase CPK Normal Range

CK-MB is the cardiac-specific isoenzyme of creatine kinase, formerly the gold standard for MI diagnosis before troponin. It rises 4-6 hours after MI, peaks at 12-24 hours, and normalizes in 2-3 days. Its faster clearance makes CK-MB useful for detecting reinfarction when troponin remains elevated from the initial event.

Also known as: LDH Blood Test for What, LDH Normal Range, LDH Values Normal

LDH is a cytoplasmic enzyme found in virtually all tissues including heart, liver, muscle, kidney, and red blood cells. When cells are damaged, LDH leaks into blood. Five isoenzymes exist: LDH-1 and LDH-2 predominate in heart and RBCs; LDH-4 and LDH-5 in liver and skeletal muscle. LDH is non-specific but useful for monitoring tissue damage, hemolysis, and certain cancers.

Also known as: Iron Saturation, What is Iron Saturation

Serum iron measures the amount of iron bound to transferrin in blood. Iron is essential for hemoglobin synthesis, oxygen transport, and enzymatic functions. Serum iron alone has limited diagnostic value due to diurnal variation and rapid changes with diet; it must be interpreted with TIBC and ferritin for complete iron status assessment.

Also known as: Serum Ferritin, Iron Stores

Ferritin is the primary iron storage protein, with small amounts released into blood reflecting total body iron stores. It's the most sensitive marker for iron deficiency—low ferritin is diagnostic. However, ferritin is also an acute phase reactant, rising with inflammation, infection, liver disease, and malignancy, which can mask underlying iron deficiency.

Also known as: TIBC Blood Test High, High Iron Binding Capacity, High Unbound Iron Binding Capacity

TIBC measures the maximum amount of iron that transferrin can bind, indirectly reflecting transferrin levels. When iron stores are depleted, the liver produces more transferrin, increasing TIBC. Conversely, in iron overload or inflammation, transferrin production decreases, lowering TIBC. TIBC and transferrin saturation are essential for complete iron status assessment.

Also known as: Cyanocobalamin

Vitamin B12 is essential for DNA synthesis, red blood cell formation, and neurological function. It's absorbed in the terminal ileum bound to intrinsic factor from stomach parietal cells. B12 deficiency causes megaloblastic anemia and neurological damage (subacute combined degeneration) that can be irreversible if untreated. Body stores last 3-5 years.

Also known as: Vitamin B9, Raised Folate Levels

Folate is a B vitamin essential for DNA synthesis and cell division. It's found in leafy greens, legumes, and fortified foods. Folate deficiency causes megaloblastic anemia identical to B12 deficiency but without neurological complications. Adequate folate before and during early pregnancy prevents neural tube defects. RBC folate reflects longer-term stores than serum folate.

Also known as: 25-OH Vitamin D, Calcidiol

Vitamin D is a fat-soluble vitamin essential for calcium absorption, bone health, immune function, and cell growth regulation. It's synthesized in skin from sun exposure and obtained from diet (fatty fish, fortified foods). 25-OH vitamin D is the best measure of vitamin D status, reflecting both dietary intake and skin synthesis. Deficiency is extremely common, especially at higher latitudes.

Testosterone is the primary male sex hormone produced mainly by testes in men and ovaries/adrenal glands in women. It regulates libido, muscle mass, bone density, red blood cell production, and mood. Total testosterone includes both bound and free forms. Free testosterone (1-2% of total) is the biologically active fraction.

Estradiol is the most potent estrogen, produced primarily by ovaries in premenopausal women. It regulates the menstrual cycle, bone density, cardiovascular health, and skin integrity. Levels fluctuate dramatically during the menstrual cycle, peaking before ovulation.

Cortisol is the primary stress hormone produced by the adrenal cortex. It regulates metabolism, immune response, blood pressure, and glucose levels. Cortisol follows a diurnal pattern, highest in the morning and lowest at midnight. Chronic elevation causes Cushing syndrome; deficiency causes Addison disease.

DHEA-S (dehydroepiandrosterone sulfate) is an adrenal androgen that serves as precursor to both testosterone and estrogen. It's the most abundant steroid hormone in circulation. DHEA-S levels decline progressively with age, leading some to supplement for anti-aging effects (though evidence is limited).

FSH is a pituitary hormone that stimulates ovarian follicle development in women and sperm production in men. FSH levels are used to evaluate fertility, menopause, and gonadal function. In menopause, ovarian feedback is lost and FSH rises dramatically.

LH is a pituitary hormone that triggers ovulation in women and stimulates testosterone production in men. The LH surge at mid-cycle triggers egg release. LH/FSH ratio is important in diagnosing PCOS, where LH is often elevated relative to FSH.

Prolactin is produced by the pituitary gland and primarily stimulates breast milk production. It also affects menstrual cycles and fertility. Stress, sleep, and meals can transiently elevate prolactin. Persistently elevated levels suggest prolactinoma or medication effect.

Insulin is produced by pancreatic beta cells to regulate glucose uptake into cells. Fasting insulin levels help assess insulin resistance, a precursor to type 2 diabetes. High fasting insulin with normal glucose indicates the body is working harder to maintain normal blood sugar.

PTH is secreted by parathyroid glands in response to low calcium. It raises blood calcium by increasing bone resorption, kidney calcium reabsorption, and vitamin D activation. PTH must be interpreted with calcium—the combination determines diagnosis.

IGF-1 is produced mainly by the liver in response to growth hormone. It mediates most of GH's growth-promoting effects. Unlike GH which fluctuates throughout the day, IGF-1 is stable and better reflects overall GH status. IGF-1 is used to diagnose GH deficiency and acromegaly.

Also known as: ANA Titer 1:320

ANA are antibodies targeting components of cell nuclei. They're screening tests for systemic autoimmune diseases, particularly lupus (SLE). ANA is reported as titer (1:40, 1:80, 1:320, etc.) and pattern (homogeneous, speckled, nucleolar, centromere). Higher titers are more clinically significant.

Rheumatoid factor is an autoantibody (usually IgM) directed against the Fc portion of IgG. While associated with rheumatoid arthritis, RF is not specific—it occurs in other autoimmune diseases, chronic infections, and even healthy elderly individuals. Anti-CCP is more specific for RA.

Anti-CCP antibodies target citrullinated proteins and are highly specific (95-98%) for rheumatoid arthritis. They can appear years before clinical RA develops and predict more aggressive, erosive disease. Anti-CCP is now part of RA classification criteria along with RF.

Also known as: hs-CRP, Elevated CRP ICD-10

CRP is an acute phase protein produced by the liver in response to inflammation. It rises rapidly (within 6 hours) and dramatically (100-1000x) with infection, tissue injury, or inflammation. High-sensitivity CRP (hs-CRP) detects lower levels for cardiovascular risk assessment.

ESR measures how fast red blood cells settle in a tube over one hour. Inflammation increases fibrinogen and immunoglobulins, which cause RBCs to stack (rouleaux) and settle faster. ESR is nonspecific but useful for monitoring chronic inflammatory conditions and diagnosing temporal arteritis/polymyalgia rheumatica.

Also known as: C3 Blood Test, C3 Complement Blood Test

C3 is the central component of the complement system, an immune defense cascade that helps destroy pathogens. Low C3 occurs when complement is consumed (active autoimmune disease) or not produced (liver disease, genetic deficiency). C3 is both an acute phase reactant and consumed in active disease.

Also known as: C4 Laboratory Test

C4 is part of the classical complement pathway, activated by antigen-antibody complexes. C4 is consumed early in immune complex diseases. Genetic C4 deficiency is common and predisposes to autoimmune disease. C4 testing helps diagnose and monitor lupus activity and hereditary angioedema.

Also known as: Elevated Haptoglobin

Haptoglobin binds free hemoglobin released from lysed red blood cells, preventing kidney damage and conserving iron. Low haptoglobin is the most sensitive marker of intravascular hemolysis. The haptoglobin-hemoglobin complex is rapidly cleared by the liver, depleting haptoglobin during hemolysis.

Also known as: Kappa Lambda Ratio, Kappa Light Chain, What Causes Elevated Kappa Free Light Chains

Free light chains (kappa and lambda) are immunoglobulin fragments produced by plasma cells. Normally, kappa slightly exceeds lambda. A skewed ratio indicates monoclonal plasma cell proliferation—one type of light chain is produced in excess. Free light chain assay is more sensitive than serum protein electrophoresis for detecting plasma cell disorders.

PSA is a protein produced by prostate cells, used for prostate cancer screening and monitoring. Elevated PSA can result from cancer, benign prostatic hyperplasia (BPH), prostatitis, or recent ejaculation. PSA density, velocity, and free/total ratio help distinguish cancer from benign causes.

Also known as: AFP Blood Test, AFP Protein Test

AFP is a fetal protein that should be minimal in healthy adults. It's a tumor marker for hepatocellular carcinoma (HCC) and certain germ cell tumors (testicular, ovarian). AFP is also used for prenatal screening—elevated maternal AFP suggests neural tube defects; low AFP suggests Down syndrome risk.

CA-125 is a protein produced by various tissues including ovarian epithelium. It's primarily used to monitor ovarian cancer treatment response and detect recurrence. CA-125 is not recommended for screening due to poor specificity—elevated in many benign conditions including endometriosis, fibroids, pregnancy, and menstruation.

CEA is a glycoprotein involved in cell adhesion, normally produced during fetal development. In adults, it's used primarily to monitor colorectal cancer treatment and detect recurrence. CEA can also be elevated in other cancers (lung, breast, pancreatic) and benign conditions (smoking, IBD, cirrhosis).

CA 19-9 is a carbohydrate antigen used primarily for pancreatic cancer diagnosis and monitoring. It's also elevated in other GI cancers (biliary, gastric, colorectal) and benign conditions (pancreatitis, biliary obstruction, cirrhosis). About 5-10% of people are Lewis antigen negative and cannot produce CA 19-9.

Also known as: pH of Pee, pH of Urine

Urine pH reflects the kidney's role in maintaining acid-base balance. The kidneys excrete hydrogen ions and reabsorb bicarbonate to regulate blood pH. Urine pH varies with diet (meat acidifies, vegetables alkalize), medications, and metabolic conditions. Persistently abnormal pH can promote kidney stone formation.

Also known as: Foamy Urine Meaning, Foaming Urine in Men/Women

Healthy kidneys prevent protein loss in urine. Proteinuria indicates glomerular damage (leaking albumin) or tubular damage (failing to reabsorb filtered proteins). Foamy urine often indicates significant proteinuria. Proteinuria is a key marker of kidney disease progression and cardiovascular risk.

Also known as: Nitrite in Urine Indicates

Nitrites in urine indicate the presence of bacteria that convert dietary nitrates to nitrites—primarily Gram-negative organisms like E. coli, Proteus, and Klebsiella. Nitrite testing requires urine to remain in the bladder for several hours for bacterial conversion, so early morning specimens are best.

Amorphous crystals are shapeless granular material found in urine sediment. Amorphous urates form in acidic urine (pink-tan color); amorphous phosphates form in alkaline urine (white). They're usually not clinically significant and often result from refrigeration of urine samples or concentrated urine.

Immature granulocytes include metamyelocytes, myelocytes, and promyelocytes—precursors to neutrophils normally found in bone marrow. Their presence in peripheral blood indicates accelerated neutrophil production, typically in response to severe infection, inflammation, or bone marrow disorders.

Nucleated RBCs are immature red cells with retained nuclei that should be absent in adult peripheral blood. Their presence indicates severe stress on erythropoiesis, bone marrow infiltration, or extramedullary hematopoiesis. Normal in newborns but pathological in adults.

ANC represents the actual number of neutrophils calculated from WBC and differential. It's the key measure for assessing infection risk in neutropenic patients. ANC = WBC × (% neutrophils + % bands) / 100.

ALC is the absolute number of lymphocytes in blood, critical for assessing immune function. It includes T-cells, B-cells, and NK cells. ALC is used in HIV monitoring and as a prognostic marker in various conditions.

Anion gap (AG) = Na - (Cl + HCO3) represents unmeasured anions in blood. It helps classify metabolic acidosis into high AG (presence of unmeasured acids) and normal AG (loss of bicarbonate) types.

Serum osmolality measures the concentration of dissolved particles. It's tightly regulated and primarily determined by sodium. Calculated osmolality = 2(Na) + Glucose/18 + BUN/2.8. The osmolar gap (measured - calculated) detects unmeasured osmoles.

Lactate is produced during anaerobic metabolism when oxygen delivery is insufficient. It's a critical marker of tissue hypoperfusion in shock and sepsis. Type A lactic acidosis results from tissue hypoxia; Type B from metabolic derangements without hypoxia.

VLDL (Very Low-Density Lipoprotein) carries triglycerides from liver to tissues. It's a precursor to LDL and is atherogenic. VLDL is usually calculated from triglycerides (TG/5) rather than directly measured.

Remnant cholesterol (calculated as TC - LDL - HDL or non-fasting TG/5) represents triglyceride-rich lipoprotein remnants that are highly atherogenic. Unlike LDL, remnants can directly enter arterial walls without oxidation, making them particularly dangerous.

Indirect (unconjugated) bilirubin is water-insoluble, bound to albumin, and cannot be excreted in urine. It's elevated when bilirubin production exceeds liver's conjugating capacity (hemolysis) or when conjugation is impaired (Gilbert syndrome, liver disease).

The albumin/globulin ratio reflects the balance between liver-produced albumin and immune-produced globulins. Ratio changes help identify liver disease (low albumin), immune disorders (high globulins), or both.

The AST/ALT ratio helps differentiate causes of liver disease. In most liver diseases, ALT exceeds AST (ratio <1). Alcoholic liver disease typically shows AST > ALT with ratio >2, due to alcohol depleting pyridoxal phosphate needed for ALT activity.

Total T4 measures both bound and free thyroxine. Since 99.97% of T4 is protein-bound (mainly to TBG), total T4 is affected by conditions altering binding proteins. Free T4 is generally preferred, but total T4 remains useful in some contexts.

Total T3 includes both bound and free forms of the most active thyroid hormone. T3 is affected by the same binding protein changes as T4. Total T3 is useful when T3 toxicosis is suspected (elevated T3 with normal T4).

Reverse T3 is an inactive metabolite of T4 produced when the body shifts T4 metabolism away from active T3. Elevated rT3 occurs in illness, calorie restriction, and stress as a protective mechanism to reduce metabolic rate.

Thyroglobulin is a protein produced only by thyroid tissue. After thyroidectomy for thyroid cancer, Tg serves as a tumor marker—any detectable level suggests residual or recurrent disease. Thyroglobulin antibodies can interfere with measurement.

TSI are antibodies that stimulate TSH receptors, causing hyperthyroidism in Graves' disease. They're specific for Graves' (not found in toxic nodular goiter) and help predict fetal/neonatal thyroid disease in pregnant women with Graves' history.

Creatinine clearance estimates GFR using 24-hour urine creatinine and serum creatinine. It's more accurate than serum creatinine alone but requires complete urine collection. Calculated as (Urine Cr × Urine volume) / (Serum Cr × time).

UACR quantifies urine albumin adjusted for urine concentration using creatinine. It's the preferred method for detecting early diabetic nephropathy and CKD. Random spot urine is convenient and correlates well with 24-hour collections.

UPCR measures total urine protein (not just albumin) adjusted for concentration. It detects both glomerular (albumin) and tubular (low molecular weight proteins) proteinuria. UPCR in mg/g approximates 24-hour protein in grams.

NT-proBNP is the inactive N-terminal fragment cleaved from proBNP. It has a longer half-life than BNP (120 vs 20 minutes) resulting in higher levels. NT-proBNP and BNP are not interchangeable but serve similar diagnostic purposes.

Troponin T is a cardiac structural protein that, along with Troponin I, is the gold standard for myocardial injury detection. High-sensitivity assays detect very low levels, enabling earlier MI detection but also detecting chronic elevations in stable cardiac conditions.

Homocysteine is an amino acid metabolite whose levels depend on vitamins B12, B6, and folate. Elevated homocysteine is associated with cardiovascular disease, stroke, and venous thrombosis, though treating with B vitamins hasn't reduced events in trials.

Vitamin A is essential for vision, immune function, skin health, and cellular differentiation. It's fat-soluble and stored in the liver. Deficiency causes night blindness and xerophthalmia; excess causes hepatotoxicity and teratogenicity.

Vitamin E is a fat-soluble antioxidant that protects cell membranes from oxidative damage. Deficiency is rare except in severe fat malabsorption (cystic fibrosis, cholestasis) and causes neurological problems including ataxia and peripheral neuropathy.

Vitamin B6 is a cofactor for over 100 enzymes, including those involved in amino acid metabolism, neurotransmitter synthesis, and heme production. Deficiency causes peripheral neuropathy, dermatitis, and microcytic anemia; excess causes sensory neuropathy.

Copper is essential for iron metabolism, connective tissue formation, and neurological function. Copper circulates bound to ceruloplasmin. Wilson disease causes copper accumulation due to impaired biliary excretion; Menkes disease causes deficiency from impaired absorption.

Selenium is a trace element essential for antioxidant enzymes (glutathione peroxidases) and thyroid hormone metabolism. Deficiency causes cardiomyopathy (Keshan disease) and muscle weakness. Selenium is important for thyroid function and immune response.

MMA is a metabolite that accumulates when vitamin B12-dependent methylmalonyl-CoA mutase is impaired. Elevated MMA is a sensitive and specific marker of functional B12 deficiency, elevated even when serum B12 is borderline or normal.

Free testosterone is the unbound, biologically active fraction (~2% of total). Conditions affecting SHBG (sex hormone-binding globulin) can cause discordance between total and free testosterone. Free testosterone better reflects androgen status when SHBG is abnormal.

SHBG is a liver-produced protein that binds testosterone and estradiol, regulating the amount available to tissues. SHBG levels are affected by many factors: increased by estrogen, thyroid hormone, liver disease; decreased by obesity, insulin resistance, androgens.

Progesterone is produced by the corpus luteum after ovulation and by the placenta during pregnancy. It prepares the endometrium for implantation and maintains early pregnancy. Progesterone testing confirms ovulation and assesses luteal phase function.

AMH is produced by ovarian follicles and reflects ovarian reserve. Unlike FSH and estradiol, AMH is stable throughout the menstrual cycle and can be measured any day. Low AMH indicates diminished ovarian reserve; very high AMH suggests PCOS.

Growth hormone is released in pulses from the pituitary, primarily during sleep. Random GH levels are difficult to interpret due to pulsatile secretion. GH deficiency is diagnosed with stimulation testing; excess (acromegaly) with suppression testing and IGF-1.

ACTH is produced by the pituitary to stimulate adrenal cortisol production. ACTH follows circadian rhythm (highest in morning). Combined with cortisol, ACTH differentiates primary adrenal disease (high ACTH, low cortisol) from pituitary/hypothalamic causes (low ACTH).

Sodium is the primary extracellular cation, essential for fluid balance, nerve function, and muscle contraction. Kidneys tightly regulate sodium levels. Abnormalities reflect water balance disorders more often than sodium intake problems.

Potassium is the primary intracellular cation, critical for cardiac conduction, muscle function, and cellular metabolism. Small changes in serum potassium significantly affect heart rhythm. Kidneys regulate potassium excretion.

Chloride is the major extracellular anion, closely linked to sodium. It helps maintain electroneutrality and acid-base balance. Chloride typically moves in the opposite direction of bicarbonate.

Bicarbonate is the body's primary buffer, maintaining blood pH between 7.35-7.45. The metabolic component of acid-base balance. On chemistry panels, "CO2" actually measures total CO2, mostly bicarbonate.

Calcium is essential for bone health, muscle contraction, nerve function, and coagulation. About 40% is protein-bound (mainly albumin), so correct for albumin: Corrected Ca = Total Ca + 0.8 × (4 - albumin).

Ionized (free) calcium is the biologically active form, unaffected by albumin levels. More accurate than total calcium, especially in critically ill patients, those with abnormal proteins, or acid-base disturbances.

Magnesium is essential for 300+ enzymatic reactions, including ATP production, DNA synthesis, and neuromuscular function. Often overlooked but critically important. Hypomagnesemia causes refractory hypokalemia and hypocalcemia.

Phosphorus is essential for ATP production, bone mineralization, and cellular signaling. Regulated by PTH, vitamin D, and FGF23. Inverse relationship with calcium. Major component of bone (85% of body phosphorus).

Hemoglobin is the oxygen-carrying protein in red blood cells. It's the primary measure for diagnosing and classifying anemia. Hemoglobin determines oxygen delivery to tissues and is the main target for transfusion decisions.

Hematocrit is the percentage of blood volume occupied by red blood cells. It roughly equals hemoglobin × 3. Affected by both RBC mass and plasma volume—dehydration falsely elevates HCT; overhydration falsely lowers it.

RBC count measures the number of red blood cells per microliter of blood. Combined with hemoglobin and hematocrit, it helps characterize anemias. RBC count can be normal or elevated in some anemias with small cells (microcytic).

WBC count measures total white blood cells, the immune system's cellular component. The differential breaks down WBC into neutrophils, lymphocytes, monocytes, eosinophils, and basophils—each with distinct functions and disease associations.

Platelets are cell fragments essential for primary hemostasis (initial clot formation). Produced by megakaryocytes in bone marrow, with ~1/3 sequestered in spleen. Lifespan is 8-10 days. Both high and low counts carry clinical significance.

MPV measures average platelet size. Young platelets are larger and more reactive. MPV helps distinguish causes of thrombocytopenia: high MPV suggests peripheral destruction (young platelets released); low MPV suggests bone marrow failure.

Fasting glucose measures blood sugar after 8+ hours without eating. It's a primary screening test for diabetes. Glucose regulation involves insulin, glucagon, cortisol, and other hormones maintaining levels within narrow range.

HbA1c reflects average blood glucose over 2-3 months (RBC lifespan). Glucose non-enzymatically attaches to hemoglobin, and the percentage reflects glycemic exposure. HbA1c doesn't require fasting and has less day-to-day variability than glucose.

BUN measures nitrogen from urea, a protein metabolism waste product. Produced in liver, filtered by kidneys. BUN is affected by protein intake, hydration status, and liver function, making it less specific for kidney function than creatinine.

Creatinine is a muscle metabolism byproduct filtered by kidneys at a constant rate. More specific for kidney function than BUN as it's less affected by diet and hydration. Serum creatinine inversely relates to GFR—it rises as kidney function declines.

eGFR estimates glomerular filtration rate from serum creatinine, age, and sex using validated equations (CKD-EPI 2021 removes race). It's the best overall measure of kidney function and determines CKD stage. eGFR guides drug dosing and predicts outcomes.

Total cholesterol includes LDL, HDL, and VLDL. While useful for initial screening, the individual components (especially LDL and non-HDL) better predict cardiovascular risk. Cholesterol is essential for cell membranes, hormones, and vitamin D synthesis.

LDL (Low-Density Lipoprotein) carries cholesterol to tissues and is the primary atherogenic lipoprotein. LDL particles penetrate arterial walls, become oxidized, and trigger plaque formation. LDL is the primary target for cardiovascular risk reduction.

HDL (High-Density Lipoprotein) performs "reverse cholesterol transport," carrying cholesterol from tissues back to liver for excretion. Epidemiologically protective against cardiovascular disease. However, raising HDL pharmacologically hasn't reduced events.

Triglycerides are fats from diet and liver synthesis, carried by VLDL and chylomicrons. Levels rise after eating (peak 4-6 hours). High triglycerides indicate metabolic syndrome and, at very high levels (>500), risk pancreatitis. Fasting sample preferred but non-fasting acceptable for initial screening.

ApoB is the protein component of all atherogenic lipoproteins (LDL, VLDL, IDL, Lp(a)). One ApoB per particle, so ApoB directly counts atherogenic particle number—a better predictor of cardiovascular risk than LDL-C, especially when LDL and TG levels discordant.

Lp(a) is an LDL-like particle with apolipoprotein(a) attached. Levels are 90% genetically determined and stable throughout life. Elevated Lp(a) is an independent, causal risk factor for ASCVD and aortic stenosis, affecting 20% of the population.

Non-HDL cholesterol (Total cholesterol - HDL) captures all atherogenic lipoproteins including LDL, VLDL, IDL, and Lp(a). It's particularly useful when triglycerides are elevated, making calculated LDL less accurate. Can be measured non-fasting.

Procalcitonin is a peptide that rises specifically in bacterial infections and sepsis. Unlike CRP, PCT remains low in viral infections and non-infectious inflammation. This selectivity makes it useful for differentiating bacterial from viral infections and guiding antibiotic therapy.

IL-6 is a pro-inflammatory cytokine that drives the acute phase response, stimulating CRP production by the liver. It rises earlier than CRP in infection/inflammation. IL-6 is involved in cytokine storm and is a therapeutic target in COVID-19 and autoimmune diseases.

While primarily an iron storage marker, ferritin is also an acute phase reactant that rises dramatically in inflammation, infection, and malignancy. Very high ferritin (>1000-10,000) suggests hemophagocytic lymphohistiocytosis (HLH), Adult-onset Still's disease, or severe systemic inflammation.

Specific gravity measures urine concentration relative to water (1.000). It reflects kidney's ability to concentrate or dilute urine. Depends on hydration status and kidney concentrating ability. Used to interpret other urinalysis findings and assess hydration.

Urine dipstick detects hemoglobin from intact RBCs (hematuria), free hemoglobin (hemolysis), or myoglobin (rhabdomyolysis). Microscopy distinguishes true hematuria (RBCs present) from hemoglobinuria/myoglobinuria (no RBCs). Hematuria can be glomerular or non-glomerular.

Leukocyte esterase is an enzyme released by white blood cells. Positive result indicates pyuria (WBCs in urine), suggesting urinary tract infection or inflammation. Combined with nitrites, it's useful for UTI screening, though culture remains the gold standard.

Glucose appears in urine when blood glucose exceeds renal threshold (~180 mg/dL) or tubular reabsorption is impaired. Historically used for diabetes monitoring before home glucose meters. Now mainly indicates uncontrolled hyperglycemia or renal tubular dysfunction.

Ketones (acetoacetate, beta-hydroxybutyrate) appear in urine during fat metabolism when glucose is unavailable or unusable. Urine dipstick detects acetoacetate only; serum beta-hydroxybutyrate is more accurate for DKA. Ketonuria occurs with fasting, DKA, alcoholic ketoacidosis, and low-carb diets.

Only conjugated (direct) bilirubin is water-soluble and appears in urine. Unconjugated bilirubin is bound to albumin and doesn't pass into urine. Bilirubinuria indicates hepatobiliary disease with elevated conjugated bilirubin—never from hemolysis alone.

MCV measures average RBC volume, classifying anemias as microcytic (<80), normocytic (80-100), or macrocytic (>100). Key for anemia differential diagnosis. See our complete RDW guide for detailed interpretation.

MCH measures average hemoglobin mass per RBC. Low MCH indicates hypochromic cells (iron deficiency, thalassemia). MCH generally parallels MCV—small cells have less hemoglobin.

MCHC is hemoglobin concentration per RBC volume. Low MCHC means hypochromic cells. MCHC rarely exceeds 36 g/dL (hemoglobin solubility limit) except in spherocytosis where cells are very small.

RDW measures variation in RBC sizes (anisocytosis). High RDW indicates mixed cell populations. Combined with MCV, RDW helps differentiate anemia causes. Iron deficiency has high RDW; thalassemia trait has normal RDW.

Reticulocytes are immature RBCs just released from bone marrow. Reticulocyte count reflects bone marrow RBC production. Essential for classifying anemia as production problem vs destruction/loss problem.

Neutrophils are the most abundant WBCs, first responders to bacterial infection. They phagocytose bacteria and release inflammatory mediators. "Left shift" means increased immature neutrophils (bands) indicating acute infection.

Lymphocytes include T-cells (cellular immunity), B-cells (antibody production), and NK cells (innate immunity). Absolute count more meaningful than percentage. Flow cytometry further characterizes lymphocyte subsets.

Monocytes are large WBCs that migrate to tissues and become macrophages. They phagocytose pathogens, present antigens, and regulate inflammation. Important in chronic infections like tuberculosis.

Eosinophils fight parasites and mediate allergic inflammation. They release granules containing cytotoxic proteins. Eosinophilia is defined as >500 cells/μL; severe eosinophilia >1500 can cause organ damage.

Basophils are the rarest WBCs, containing histamine and heparin granules. They play roles in allergic reactions and parasitic immunity. Basophilia is often associated with myeloproliferative neoplasms.

Direct (conjugated) bilirubin is water-soluble and can be excreted in urine. It's elevated in hepatocellular disease and biliary obstruction. Direct bilirubin >50% of total indicates hepatobiliary pathology rather than hemolysis.

Prealbumin (transthyretin) is a transport protein for thyroid hormone and vitamin A. With its short half-life (2 days), it responds quickly to nutritional changes, making it a marker of recent protein status and acute nutritional changes.

Ammonia is produced from protein metabolism and normally converted to urea by the liver. In liver failure, ammonia accumulates and crosses the blood-brain barrier, causing hepatic encephalopathy. Sample handling critical—process immediately on ice.

hCG is produced by placental trophoblasts during pregnancy and by certain tumors (gestational trophoblastic disease, testicular germ cell tumors). Quantitative hCG is essential for early pregnancy monitoring and tumor marker surveillance.

CA 15-3 is a mucin glycoprotein used to monitor breast cancer treatment response and detect recurrence. Not useful for screening due to low sensitivity in early disease. Elevated in metastatic breast cancer in 50-70% of cases.

CA 27.29, like CA 15-3, is a mucin marker used in breast cancer monitoring. It detects the same MUC1 protein but with different epitopes. Either marker (not both) can be used for monitoring—similar clinical utility.

Thrombin time measures the final step of coagulation: thrombin converting fibrinogen to fibrin. It's independent of intrinsic and extrinsic pathways. Prolonged TT indicates fibrinogen problems or thrombin inhibition.

Antithrombin is the main inhibitor of thrombin and factor Xa. It's essential for heparin's anticoagulant effect. AT deficiency is an inherited thrombophilia that causes venous thromboembolism, often in unusual sites.

Protein C is a vitamin K-dependent anticoagulant that, when activated by thrombin-thrombomodulin, inactivates factors Va and VIIIa. Protein C deficiency increases VTE risk. Warfarin initially lowers Protein C, risking warfarin-induced skin necrosis.

Protein S is a vitamin K-dependent cofactor for activated Protein C. Only free Protein S (40%) is active; the rest binds C4b-binding protein. Protein S deficiency is an inherited thrombophilia. Estrogen lowers Protein S levels.

Factor V Leiden is a genetic mutation making Factor V resistant to inactivation by activated Protein C. Most common inherited thrombophilia in Caucasians (5%). Heterozygotes have 5-10x VTE risk; homozygotes 50-100x risk.

Anti-dsDNA antibodies are highly specific (95%) for systemic lupus erythematosus. They correlate with disease activity, especially lupus nephritis. Rising titers often precede flares. Present in 50-70% of SLE patients.

Anti-Smith antibodies are highly specific (99%) for SLE but have low sensitivity (25-30%). They target snRNP proteins involved in mRNA processing. Unlike anti-dsDNA, anti-Sm titers don't correlate with disease activity.

Anti-SSA (Ro) and Anti-SSB (La) are extractable nuclear antigens found in Sjögren syndrome and SLE. Anti-SSA is more common and associated with neonatal lupus and congenital heart block when present in pregnant women.

Anti-Scl-70 targets DNA topoisomerase I and is specific for systemic sclerosis (scleroderma), particularly diffuse cutaneous disease. Associated with increased risk of interstitial lung disease and more severe disease course.

Anticentromere antibodies target centromeric proteins and are highly specific for limited cutaneous systemic sclerosis (CREST syndrome). Associated with less severe skin and lung disease but increased pulmonary arterial hypertension risk.

ANCA are autoantibodies against neutrophil granule proteins. c-ANCA (cytoplasmic, anti-PR3) is associated with GPA (Wegener's); p-ANCA (perinuclear, anti-MPO) with MPA and EGPA. Essential for diagnosing ANCA-associated vasculitis.

Anti-GBM antibodies target the alpha-3 chain of type IV collagen in glomerular and alveolar basement membranes. They cause Goodpasture syndrome (pulmonary hemorrhage + rapidly progressive glomerulonephritis). A medical emergency requiring plasmapheresis.

Aldosterone is a mineralocorticoid produced by the adrenal zona glomerulosa. It regulates sodium retention and potassium excretion, controlled by RAAS. Aldosterone/renin ratio (ARR) screens for primary aldosteronism, the most common secondary hypertension cause.

Renin is released by kidney juxtaglomerular cells in response to low blood pressure, low sodium, or sympathetic stimulation. It converts angiotensinogen to angiotensin I, initiating the RAAS cascade. Renin measurement helps classify hypertension causes.

17-hydroxyprogesterone is a precursor in cortisol and androgen synthesis. Elevated levels indicate 21-hydroxylase deficiency (most common cause of congenital adrenal hyperplasia, CAH). Used in newborn screening and evaluating hirsutism/PCOS for nonclassic CAH.

Androstenedione is an androgen precursor produced by adrenal glands and gonads, converted to testosterone and estrogen peripherally. Elevated in women with hyperandrogenism. Helps distinguish ovarian from adrenal androgen excess.

Zinc is essential for enzyme function, immune response, wound healing, and taste/smell. Deficiency is common in malnutrition, malabsorption, chronic illness, and alcoholism. Serum zinc is not always reliable as it's a negative acute phase reactant.

Thiamine is essential for carbohydrate metabolism and nerve function. Deficiency causes beriberi (cardiac/neurologic) and Wernicke-Korsakoff syndrome in alcoholics. Always give thiamine BEFORE glucose in suspected deficiency to prevent precipitating Wernicke's.

Vitamin C is essential for collagen synthesis, antioxidant function, and iron absorption. Humans cannot synthesize it (unlike most mammals). Deficiency causes scurvy with impaired wound healing, gum disease, and hemorrhage. Rare in developed countries except alcoholics and restricted diets.

Vitamin K is essential for synthesizing clotting factors II, VII, IX, X and proteins C and S. Obtained from leafy greens (K1) and gut bacteria (K2). Deficiency causes coagulopathy with elevated PT/INR. Newborns are deficient—prophylactic vitamin K at birth prevents hemorrhagic disease.