Biomarkers

ALT (alanine aminotransferase) is an enzyme primarily found in liver cells (hepatocytes). Released into the bloodstream when liver cells are stressed, it is one of the most commonly measured parameters in biology for assessing liver function. ALT measurement is part of the standard liver panel.

Apolipoprotein B (ApoB) is the main structural protein of LDL, VLDL, IDL and Lp(a) lipoproteins. Each of these lipoprotein particles contains exactly one ApoB molecule, making ApoB measurement a direct reflection of the number of circulating lipoprotein particles. This parameter is increasingly included in comprehensive lipid panels, complementing classic LDL cholesterol.

Combined estimated glomerular filtration rate (combined eGFR) is calculated from creatinine and cystatin C using the CKD-EPI 2021 equation (Inker et al.). This combined formula provides a more accurate estimate of kidney function than creatinine or cystatin C alone, as it integrates two markers with complementary properties. The calculation takes into account both age and biological sex.

Copper is an essential trace element, cofactor for many enzymes in the body. Its blood measurement is often interpreted alongside zinc, as the two elements are metabolically linked. Copper is naturally present in the liver, brain and kidneys.

The copper-to-zinc ratio reflects the balance between these two essential trace elements, which share common absorption pathways and exert reciprocal influence. This ratio is increasingly monitored in nutritional biology, as the two elements are closely interdependent: a change in one influences the status of the other.

Creatinine is a metabolic waste product from muscles, eliminated by the kidneys. Its blood level is a key indicator of kidney function. Elevated creatinine may signal impaired glomerular filtration. This biomarker is used as a component of the CKD-EPI 2021 equation to estimate glomerular filtration rate (GFR).

Cystatin C is a protein produced at a constant rate by all nucleated cells and eliminated exclusively by glomerular filtration. Unlike creatinine, its level is not influenced by muscle mass, sex, or diet, making it a more reliable marker of kidney function. It is used in the combined CKD-EPI 2021 equation for a more precise estimation of GFR.

Fasting blood glucose measures blood sugar concentration after 8 to 12 hours of fasting. It is one of the most fundamental parameters of carbohydrate metabolism, routinely measured in virtually all blood panels. Fasting glucose reflects glucose regulation at rest, in the absence of recent food intake.

Fasting insulin measures circulating insulin concentration after 8 to 12 hours of fasting. Insulin is the hormone secreted by the pancreas (beta cells of the islets of Langerhans) in response to blood glucose. Its fasting measurement reflects basal insulin production, outside of any dietary stimulation. Combined with fasting glucose, it allows calculation of the HOMA-IR index.

Ferritin is the main iron storage protein in the body. Its blood measurement reflects iron reserves more reliably than serum iron alone. It is the first-line parameter for assessing iron status — both deficiency and overload situations.

GGT (gamma-glutamyltransferase) is an enzyme involved in glutathione metabolism, primarily found in the liver, kidneys and pancreas. Its blood measurement is one of the most sensitive liver parameters and is part of the standard hepatic panel. GGT responds to numerous factors, making it a broad metabolic indicator.

HbA1c (glycated hemoglobin) reflects average blood glucose over the past 2 to 3 months. Unlike fasting glucose (a snapshot), HbA1c provides an overview of long-term glucose exposure. It forms naturally through non-enzymatic binding of glucose to red blood cell hemoglobin, proportionally to ambient blood sugar.

HDL cholesterol is a high-density lipoprotein involved in reverse cholesterol transport — carrying cholesterol from peripheral tissues back to the liver. Often distinguished from LDL in lipid panels, HDL is one of the most systematically measured parameters in lipid profile assessment.

Hemoglobin is the red blood cell protein responsible for transporting oxygen from the lungs to all body tissues. Its measurement reflects the blood's capacity to ensure tissue oxygenation. It is one of the most fundamental parameters of the complete blood count (CBC).

HOMA-IR (Homeostatic Model Assessment for Insulin Resistance) is an index calculated from fasting insulin and glucose using the formula: (Insulin [µIU/mL] × Glucose [mg/dL]) / 405. It evaluates the relationship between insulin production by the pancreas and tissue response to that insulin. It is an increasingly used parameter in comprehensive metabolic panels.

Homocysteine is a sulfur-containing amino acid intermediate of the methylation cycle, at the crossroads of vitamin B9, B12 and B6 metabolism. Its measurement reflects the proper functioning of the methylation cycle — one of the body's most fundamental biochemical processes, involved in gene expression regulation and amino acid metabolism.

High-sensitivity C-reactive protein (hs-CRP) is a low-grade inflammation marker produced by the liver. Unlike standard CRP (which detects acute inflammation), hs-CRP is measured with enhanced sensitivity to detect very low levels of chronic inflammation. It is increasingly included in preventive health panels.

Red blood cell (RBC) magnesium reflects long-term magnesium reserves, unlike serum magnesium which represents only 1% of total body magnesium and fluctuates rapidly. Magnesium is a cofactor for over 300 enzymatic reactions. This erythrocyte measurement provides a more accurate picture of true magnesium status.

Mean Corpuscular Volume (MCV) measures the average size of red blood cells, expressed in femtoliters (fL). This parameter is part of the standard complete blood count (CBC). MCV reflects red blood cell production dynamics in the bone marrow and can be influenced by vitamin B9, B12 and iron status.

Platelet count (thrombocyte count) is part of the standard complete blood count. Platelets are cell fragments produced by the bone marrow, involved in blood clotting. Their number reflects the balance between medullary production and peripheral consumption, and varies according to numerous physiological factors.

Selenium is an essential trace element, incorporated in the body as selenocysteine within 25 selenoproteins identified in humans, including glutathione peroxidases and thyroid deiodinases. Its blood measurement assesses the status of this trace element whose requirements and dietary intake vary considerably by geographic region.

Transferrin saturation (TSAT) measures the percentage of transferrin — the iron transport protein in the blood — actually loaded with iron. It is a more informative parameter than serum iron alone, as it reflects the functional availability of iron to tissues. It is part of the complete iron panel, alongside ferritin.

Triglycerides are the main storage form of fatty acids in the body, transported in the blood by lipoproteins (VLDL, chylomicrons). Their fasting measurement is part of the standard lipid panel. Triglyceride levels are closely linked to recent diet, meal composition and carbohydrate metabolism.

TSH (thyroid stimulating hormone) is the hormone produced by the pituitary gland to regulate thyroid gland activity. It acts as a thermostat: when thyroid hormones are circulating in sufficient quantity, TSH decreases; when they are insufficient, TSH increases. Its measurement is the first-line parameter for assessing thyroid function.

Vitamin B12 (cobalamin) is an essential water-soluble vitamin involved in DNA synthesis, amino acid metabolism and the methylation cycle. Its blood measurement assesses B12 reserves — a vitamin exclusively of animal or bacterial origin, whose absorption depends on gastric intrinsic factor and naturally decreases with age.

Folate (vitamin B9) is essential for DNA synthesis and the methylation cycle, where it works synergistically with vitamin B12. Serum or red blood cell folate measurement assesses the status of this vitamin, whose requirements vary between individuals, particularly based on genetic profile (MTHFR polymorphisms).

25-OH vitamin D (calcidiol) is the circulating form of vitamin D, produced by the liver from vitamin D3 (cutaneous or dietary). Its measurement is the most reliable reflection of vitamin D status, with a plasma half-life of 2 to 3 weeks. Vitamin D deficiency is one of the most widespread nutritional deficiencies worldwide, particularly at temperate latitudes.

Zinc is an essential trace element, structurally involved in over 300 enzymes and approximately 10% of all human proteins ("zinc finger" proteins). Its blood measurement assesses zinc status, whose body reserves are limited (there is no mobilizable "stock" as with iron). Zinc is often measured alongside copper.