Biomarkers

8-OHdG (8-hydroxy-2'-deoxyguanosine) is an oxidatively modified nucleoside formed when reactive oxygen species (ROS) attack the C8 position of guanine in DNA; it is among the…

Albumin is the most abundant plasma protein, synthesized exclusively by the liver, and maintains colloid osmotic pressure while transporting hormones, fatty acids, calcium,…

The albumin/globulin ratio (A/G ratio) is calculated from total protein and albumin measurements as albumin divided by (total protein minus albumin), with the globulin fraction…

Alkaline phosphatase (ALP) is a hydrolase enzyme that cleaves phosphate groups at alkaline pH and is measured in serum as a composite of isoforms originating primarily from the…

Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are intracellular enzymes released into blood when hepatocytes are injured. ALT is relatively liver-specific,…

Apolipoprotein A-I is a 28-kDa hepatic and intestinal apolipoprotein that constitutes about 70% of total HDL protein and activates lecithin-cholesterol acyltransferase (LCAT),…

Apolipoprotein B (ApoB) is the structural protein of atherogenic lipoproteins, including LDL, VLDL, IDL, and Lp(a). Because ApoB-100 is typically present as approximately one…

Apolipoprotein E (APOE) is a lipid-transport protein encoded by the APOE gene, which segregates into three alleles — ε2, ε3, and ε4 — producing six possible genotypes. The ε4…

The AST/ALT ratio, also called the De Ritis ratio after Fernando De Ritis who first described its diagnostic utility in the 1950s, is calculated as aspartate aminotransferase…

Bilirubin is the predominant end-product of haem catabolism, formed when reticuloendothelial cells degrade senescent red blood cells; it circulates as unconjugated (indirect)…

C-peptide is the 31-amino-acid chain excised from proinsulin in pancreatic beta cells. One molecule is co-secreted per insulin molecule, so fasting C-peptide directly reflects…

CA-125 (cancer antigen 125) is a high-molecular-weight mucin-like glycoprotein encoded by MUC16 and expressed on coelomic and Müllerian-derived epithelium; it is shed into the…

Cell-free DNA refers to short (typically 140-200 bp mono-nucleosome and 300-400 bp di-nucleosome) double-stranded DNA fragments released into plasma by apoptotic and necrotic…

The coronary artery calcium (CAC) score is a non-contrast cardiac CT measurement reported as an Agatston score that quantifies calcified atherosclerotic plaque as a marker of…

Cortisol is the primary glucocorticoid of the adrenal cortex, the end-effector of the hypothalamic–pituitary–adrenal (HPA) axis. It follows a pronounced diurnal rhythm: levels…

Creatine kinase (CK) is an enzyme that catalyses the reversible transfer of a phosphate group from phosphocreatine to ADP, regenerating ATP in tissues with high and fluctuating…

Creatinine is a breakdown product of muscle creatine, produced at a relatively constant rate and cleared predominantly by glomerular filtration with a small contribution from…

Cystatin C is a small (13 kDa) cysteine protease inhibitor produced at a constant rate by all nucleated cells, freely filtered by the glomerulus, and almost entirely reabsorbed…

D-dimer is a cross-linked fibrin degradation product generated when plasmin cleaves stabilised fibrin, and serves as a global marker of activated coagulation and fibrinolysis. It…

Dehydroepiandrosterone sulfate (DHEA-S) is the sulfated, long-circulating form of DHEA, secreted by the adrenal cortex (zona reticularis) and serving as a precursor to androgens…

Estradiol (E2) is the most biologically active estrogen, produced mainly in the ovaries before menopause and in smaller amounts via aromatization of androgens in adipose tissue,…

F2-isoprostanes are a family of prostaglandin F2α-like compounds formed non-enzymatically by free radical-mediated peroxidation of arachidonic acid esterified in phospholipids;…

Fasting glucose is the plasma blood-sugar concentration after at least eight hours without caloric intake. It reflects baseline glucose homeostasis driven by hepatic glucose…

Fasting insulin measures circulating insulin after an overnight fast and reflects β-cell output, hepatic insulin clearance, and peripheral insulin sensitivity together. Elevated…

Ferritin is a ubiquitous intracellular iron-storage protein that releases a small fraction into circulation; serum ferritin is therefore the most widely used biomarker for…

Fibrinogen (coagulation factor I) is a hepatically produced 340-kDa glycoprotein that polymerises to fibrin during clot formation and is also an acute-phase reactant. It is…

Free T3 (fT3) and free T4 (fT4) are the unbound, biologically active fractions of triiodothyronine and thyroxine. T4 is the main thyroid secretion product and is deiodinated…

Free testosterone is the 1-4% of circulating testosterone not bound to SHBG or albumin and represents the immediately bioactive fraction. The gold-standard analytical method is…

Fructosamine denotes glycated serum proteins — chiefly albumin — formed via non-enzymatic glucose binding and Amadori rearrangement to a stable ketoamine. Albumin's ~14–21-day…

Galectin-3 is a 30-kDa beta-galactoside-binding lectin secreted by activated macrophages that drives myocardial fibroblast proliferation, collagen deposition and adverse cardiac…

Glial fibrillary acidic protein is the principal intermediate filament of mature astrocytes and a marker of reactive astrogliosis. Ultrasensitive immunoassays allow measurement…

Gamma-glutamyl transferase (GGT) is a membrane-bound enzyme that transfers gamma-glutamyl groups and supports glutathione recycling, with highest activity in liver, biliary…

GlycA is a composite nuclear magnetic resonance (NMR) spectroscopy signal arising predominantly from N-acetyl methyl groups on acute-phase glycoproteins — primarily α1-acid…

HDL cholesterol (high-density lipoprotein cholesterol) measures the cholesterol carried by HDL particles, which transport cholesterol from tissues back to the liver in reverse…

High-sensitivity troponin (hs-Tn) assays measure the cardiac isoforms troponin I (hs-TnI) or troponin T (hs-TnT) at concentrations about 10-fold lower than conventional assays,…

Homocysteine is a sulfur-containing amino acid produced during methionine metabolism and cleared via remethylation or transsulfuration pathways that depend on folate, vitamin…

High-sensitivity C-reactive protein (hs-CRP) is a liver-produced acute-phase protein, induced primarily by IL-6, and measured with an assay sensitive enough to detect low-grade…

Insulin-like growth factor 1 (IGF-1) is produced mainly in the liver under growth hormone stimulation and mediates many anabolic GH effects on muscle, bone, and other tissues. As…

Interleukin-6 (IL-6) is a pleiotropic cytokine produced by immune cells, adipocytes, endothelial cells, and senescent cells that signals through the membrane-bound IL-6 receptor…

Ionized calcium (iCa²⁺), also called free calcium, is the biologically active fraction of total serum calcium, comprising approximately 45–50% of the total and not bound to…

LDL cholesterol (low-density lipoprotein cholesterol) reflects the cholesterol carried by LDL particles in the bloodstream. Excess ApoB-containing LDL particles can enter and be…

LDL-P, or LDL particle number, quantifies the total concentration of low-density lipoprotein particles in plasma rather than their cholesterol payload, typically measured by…

Lp-PLA2 (platelet-activating factor acetylhydrolase) is a calcium-independent enzyme secreted mainly by macrophages and lymphocytes; in plasma roughly 80% circulates bound to…

Lipoprotein(a) is an LDL-like particle in which apolipoprotein(a) is covalently linked to apoB-100 via a disulfide bond. Plasma levels are largely (often cited around 70–90%)…

The absolute lymphocyte count (ALC) is the total number of circulating lymphocytes — comprising T cells, B cells, and NK cells — derived from a complete blood count differential.…

Serum magnesium reflects the small circulating fraction of total body magnesium, with roughly 99% stored in bone, muscle, and soft tissue, making serum levels an insensitive…

Multi-cancer early detection (MCED) tests are blood assays interrogating plasma cell-free DNA - chiefly methylation patterns and fragmentomics - to detect a shared "cancer…

Myeloperoxidase is a heme-containing peroxidase stored in azurophilic granules of neutrophils and monocytes that generates hypochlorous acid and other reactive oxidants during…

The neutrophil-lymphocyte ratio (NLR) is derived from a standard complete blood count as the absolute neutrophil count divided by the absolute lymphocyte count, with a typical…

Neurofilament light chain is a cytoskeletal protein of large myelinated axons released into cerebrospinal fluid and blood upon neuroaxonal injury. Ultrasensitive single-molecule…

Non-HDL cholesterol (non-HDL-C) equals total cholesterol minus HDL and captures the cholesterol in all atherogenic lipoproteins — LDL, VLDL, IDL, chylomicron remnants, and Lp(a).…

N-terminal pro-B-type natriuretic peptide (NT-proBNP) is the biologically inactive N-terminal fragment cleaved from proBNP when cardiomyocytes are stretched by elevated…

The Omega-3 index is a blood biomarker defined as the sum of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) expressed as a percentage of total fatty acids in red…

Oxidized LDL (oxLDL) refers to LDL particles in which the polyunsaturated fatty acids and apolipoprotein B-100 have undergone oxidative modification, typically within the…

p-tau217 is tau protein phosphorylated at threonine 217 and the most Alzheimer-specific plasma biomarker currently available. Concentrations rise early along the amyloid cascade,…

Serum inorganic phosphate reflects the balance between intestinal absorption, renal tubular reabsorption, and exchange with bone and intracellular stores, regulated principally…

Prostate-specific antigen (PSA) is a serine protease of the kallikrein family produced almost exclusively by prostatic epithelial cells; it liquefies seminal coagulum but leaks…

Red cell distribution width (RDW) is a quantitative measure of the variability in erythrocyte volume (anisocytosis), reported as the coefficient of variation of the erythrocyte…

Remnant cholesterol is the cholesterol content of triglyceride-rich lipoprotein (TRL) remnants — primarily VLDL and IDL in the fasting state, and chylomicron remnants…

Reverse T3 (3,3',5'-triiodothyronine) is the biologically inactive isomer of T3 produced when 5-deiodinase type 3 (D3) cleaves the inner ring of T4 instead of the outer ring.…

SHBG is a liver-synthesised glycoprotein that binds approximately 98% of circulating testosterone and 30-60% of estradiol with high affinity, regulating the bioavailable hormone…

Small dense LDL (sdLDL) is a subfraction of LDL particles characterised by reduced diameter (less than approximately 25.5 nm) and higher density compared with large buoyant LDL,…

Testosterone is the principal androgen, produced mainly by Leydig cells in the testes in men and in smaller amounts by the ovaries and adrenals in women. It supports muscle mass,…

Anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (TgAb) antibodies target intrathyroidal enzymes and are the principal serologic markers of autoimmune thyroid disease.…

Transferrin saturation (TSAT) is the percentage of iron-binding sites on transferrin — the main iron-transport protein in blood — occupied by iron, calculated as (serum iron ÷…

Triglycerides are the main storage form of dietary and endogenous fat, transported in the blood by triglyceride-rich lipoproteins, mainly VLDL, chylomicrons, IDL, and their…

Thyroid-stimulating hormone (TSH) is released by anterior pituitary thyrotrophs and regulates thyroid hormone production via negative feedback from circulating T3 and T4. In…

The TyG index is a surrogate marker for insulin resistance calculated as ln(fasting triglycerides [mg/dL] × fasting glucose [mg/dL] ÷ 2). Proposed by Simental-Mendía et al. in…

Uric acid is the final catabolic product of purine metabolism in humans, produced mainly in the liver by xanthine oxidase and excreted predominantly by the kidney (~70%) with the…

The urine albumin-to-creatinine ratio (UACR) quantifies albumin leaking into urine relative to urinary creatinine, correcting for hydration status. A healthy glomerular…

Vitamin B12 (cobalamin) and folate (vitamin B9) are essential coenzymes in one-carbon metabolism: B12 is required for methionine synthase (which regenerates methionine from…

25-hydroxyvitamin D (25-OH-D, calcidiol) is the major circulating form of vitamin D and the standard clinical biomarker for assessing vitamin D status, produced in the liver by…