Biomarkers: reference ranges and what affects them

Each reference page explains what the marker is, which ranges laboratories commonly report, why a result can be high or low, and how to prepare for the test. Values are given in conventional units with SI units alongside.

Blood cells

Hemoglobin

The iron-rich protein in red blood cells that carries oxygen from the lungs to every tissue. The core marker checked whenever anemia is suspected.

White blood cells (WBC)

The immune cells that defend the body against infection. The count rises or falls with infections, inflammation, medicines, and bone marrow conditions.

Red blood cells (RBC)

The cells that carry oxygen from the lungs to every tissue. The count is the first line checked when anemia is suspected.

Platelets (PLT)

The cell fragments that stop bleeding by forming clots. Too few raises bleeding risk, too many — the risk of clots.

Hematocrit (Hct)

The share of blood volume taken up by red blood cells. Falls in anemia and blood loss, rises with dehydration and hypoxia.

ESR (sedimentation rate)

How fast red cells settle in a tube — a nonspecific gauge of inflammation somewhere in the body.

Neutrophils

The most abundant white blood cells — the first line of defense against bacteria. Rise in bacterial infections and stress; fall after viral infections and with bone marrow suppression.

Lymphocytes

The cells of immune memory and antiviral defense. Rise in viral infections; fall with stress, immunodeficiency and steroids.

Monocytes

The largest blood cells — the cleanup crew of inflamed tissue. Rise during recovery from infections and in chronic inflammation.

Eosinophils

The cells of allergic reactions and anti-parasite defense. Rise in allergy, asthma, helminth infections and some skin diseases.

Basophils

The rarest white blood cells — participants of allergic reactions. Marked growth is uncommon and needs a hematologist's review.

Blood chemistry

Blood glucose

The main sugar in the blood and the body's key fuel. The fasting level is the standard screening number for prediabetes and diabetes.

Hemoglobin A1C (HbA1c)

The share of hemoglobin coated with glucose — an average picture of blood sugar over the past two to three months.

ALT (alanine transaminase)

A liver enzyme that leaks into the blood when liver cells are injured.

AST (aspartate transaminase)

An enzyme of the liver, heart, and muscles that rises when those tissues are injured.

Gamma-glutamyl transferase

A liver and bile duct enzyme, sensitive to alcohol and to blocked bile flow.

Alkaline phosphatase (ALP)

An enzyme of liver, bile ducts, and bone; the source of a high value needs a second look.

LDH (lactate dehydrogenase)

A general tissue-damage enzyme found in the heart, liver, muscles, and many other tissues.

Bilirubin

The yellow pigment behind jaundice, processed by the liver from old red blood cells.

Amylase

A digestive enzyme of the pancreas and salivary glands; the classic pancreatitis marker.

Creatinine

A muscle-waste product filtered entirely by the kidneys; the core kidney function marker.

BUN (blood urea nitrogen)

The nitrogen waste of protein breakdown, filtered by the kidneys; read together with creatinine.

Uric acid

The end product of purine breakdown; high levels are linked to gout and kidney stones.

Total protein

The combined albumin and globulin in blood serum; a window on nutrition, liver, and kidneys.

Albumin

The main blood protein, made by the liver; carries molecules and holds fluid in vessels.

Calcium

A mineral of bones, nerves, muscles, and heart, tightly controlled by the parathyroid glands.

Potassium

The electrolyte that keeps nerves, muscles, and the heart's rhythm working.

Sodium

The electrolyte that governs the body's water balance and nerve and muscle function.

Total cholesterol

The sum of all cholesterol types in the blood, measured within the lipid profile.

LDL cholesterol

The “bad” cholesterol: its excess settles in artery walls as plaque.

HDL cholesterol

The “good” cholesterol: it carries cholesterol back to the liver for removal.

Triglycerides

The fat in which the body stores spare calories; measured with cholesterol.

C-reactive protein (CRP)

A liver-made protein that rises with inflammation anywhere in the body.

Magnesium

An electrolyte for muscles, nerves and the heart. Deficiency shows as cramps and weakness; excess occurs mainly in kidney failure.

C-peptide

A byproduct of the body's own insulin production. Shows how much insulin the pancreas makes and helps tell diabetes types apart.

Apolipoprotein A-I (ApoA1)

The main protein of HDL particles. Higher levels are associated with lower cardiovascular risk.

Apolipoprotein B (ApoB)

One molecule per atherogenic particle — ApoB counts LDL and VLDL particles directly, often more informative than LDL cholesterol.

Lipoprotein(a) — Lp(a)

A genetically determined atherogenic particle — an independent inherited risk factor for heart attack, stroke, and aortic stenosis.

Atherogenic coefficient

A calculated index — (total cholesterol − HDL) / HDL — summarizing the balance of bad and good lipoproteins.

Homocysteine

A methionine-cycle amino acid. Elevated levels are linked to vascular risk and to folate and B12 deficiency.

Fructosamine

Glycated serum proteins — the average glucose of the last 2–3 weeks. Complements HbA1c when it is uninformative.

Glucose tolerance test (OGTT)

The 75 g glucose challenge: detects impaired glucose tolerance and diabetes when fasting glucose is still normal. Standard for gestational diabetes.

HOMA-IR insulin resistance

A calculated index of insulin sensitivity: fasting glucose × fasting insulin / 22.5. An early marker of insulin resistance.

Interleukin-6 (IL-6)

A key inflammation cytokine that triggers CRP production. A supplementary marker in infectious, autoimmune, and oncologic settings.

Procalcitonin (PCT)

A marker of systemic bacterial infection and sepsis. Helps distinguish bacterial from viral inflammation.

Iron status

Ferritin

A protein that stores iron. The ferritin level shows how much iron the body keeps in reserve — the earliest marker of iron deficiency, long before anemia develops.

Iron (serum)

The mineral behind hemoglobin; serum iron is one of several iron-status tests.

Transferrin

The iron-transport protein of blood. Rises in iron deficiency, falls in inflammation and malnutrition.

Total iron-binding capacity

How much iron all the transferrin in blood could bind. Rises in iron deficiency, falls in inflammation and iron overload.

Transferrin saturation (TSAT)

The percentage of transferrin's iron seats actually occupied: serum iron / TIBC × 100%. A key iron-metabolism figure.

Soluble transferrin receptor

A marker of the cells' demand for iron. Unlike ferritin, barely affected by inflammation — it unmasks hidden iron deficiency.

Hepcidin

The liver hormone that masters iron metabolism — it gates both absorption and release from stores. A marker for distinguishing anemias.

Thyroid

TSH (thyrotropin)

The pituitary hormone that tells the thyroid how hard to work — the first-line test of thyroid function.

Free T4

The unbound, active fraction of the main thyroid hormone, always read together with TSH.

Free T3

The unbound fraction of triiodothyronine, the hormone that sets the pace of metabolism.

TPO antibodies

Antibodies against thyroid peroxidase — the marker that shows whether an autoimmune disease is attacking the thyroid.

Anti-thyroglobulin antibodies

Antibodies against the thyroid protein thyroglobulin — a sign of autoimmune thyroid disease that also interferes with thyroglobulin measurement.

TSH receptor antibodies

The antibodies that cause Graves' disease. They confirm the diagnosis, predict relapse, and matter in pregnancy.

Thyroglobulin

The thyroid's storage protein. Its main use is follow-up after surgery for differentiated thyroid cancer — always read with anti-Tg antibodies.

Calcitonin

A hormone of the thyroid's C-cells and the key marker of medullary thyroid cancer — used for both diagnosis and follow-up.

Vitamins

Vitamin D

The vitamin of sunlight and bones: the test measures 25-hydroxyvitamin D, the storage form in the blood.

Vitamin B12

The vitamin of nerves and blood cells: deficiency first shows up as anemia or tingling in the hands and feet.

Folic acid

Vitamin B9, needed to build red blood cells and DNA — and critical before and during pregnancy.

Hormones

Insulin

The pancreatic hormone that moves glucose from the blood into the cells — read only together with blood glucose.

Cortisol

The stress hormone of the adrenal glands — its level depends on the time of day, so the hour of the draw matters.

Testosterone

The main male sex hormone — present in women too, where an elevated level is the more telling finding.

Estradiol

The main estrogen — in women its level moves with the menstrual cycle, in men it stays low and steady.

Progesterone

The hormone of the cycle's second half and of pregnancy — the day of the draw decides what the number means.

Prolactin

The milk-production hormone of the pituitary — normally low outside pregnancy and breastfeeding.

Luteinizing hormone

The pituitary hormone that triggers ovulation in women and testosterone production in men.

Follicle-stimulating hormone

The pituitary hormone that grows eggs in women and sperm in men — and the classic marker of menopause.

hCG

The pregnancy hormone produced by the embryo's outer layer. Its level and trend confirm pregnancy and track its progress.

AMH

A marker of ovarian reserve — the remaining egg supply in the ovaries. Falls with age; rises in polycystic ovary syndrome.

17-OH progesterone

An adrenal steroid intermediate — the key test for congenital adrenal hyperplasia and a marker of androgen excess in women.

DHEA sulfate (DHEA-S)

The most abundant adrenal androgen. Its long half-life makes it a stable marker of adrenal androgen production in women and children.

Sex hormone-binding globulin

The liver protein that carries testosterone and estradiol — it determines how much testosterone is actually free to act.

Free testosterone

The unbound, active 1–3% of testosterone. Reflects androgen status more accurately than total testosterone at borderline values.

Parathyroid hormone (PTH)

The master regulator of calcium. Interpreted only together with blood calcium and vitamin D.

Blood clotting

INR

A standardized measure of blood clotting based on prothrombin time. The key test for monitoring warfarin and other vitamin K antagonists.

aPTT

The seconds blood takes to clot via the intrinsic pathway. Checked before surgery, for unexplained bruising and to monitor heparin.

Fibrinogen

The plasma protein that becomes fibrin, the scaffold of a clot. Rises with inflammation and clotting risk; falls in severe bleeding disorders.

D-dimer

A fibrin breakdown product — a marker that a clot has formed and dissolved. A negative result helps rule out thrombosis.

Antithrombin III

The body's main natural anticoagulant protein. Low activity raises the risk of blood clots, including inherited thrombophilia.

Prothrombin time

Core test of the extrinsic clotting pathway and the basis for the INR — the standard monitor of warfarin therapy.

Thrombin time

Tests the final step of clotting — the conversion of fibrinogen to fibrin. Prolonged by heparin, low fibrinogen, and fibrin breakdown products.

Lupus anticoagulant

An antiphospholipid antibody that prolongs clotting tests in the tube but raises clot risk in the body. Positivity must be confirmed after 12 weeks.

Tumor markers

PSA

A protein of the prostate gland — a marker of prostate health in men. Rises with BPH, prostatitis and prostate cancer; by itself it never makes the diagnosis.

CA-125

A protein marker most often checked when an ovarian mass is found. It also rises in benign conditions — endometriosis, inflammation, menstruation.

AFP

A protein normally produced by the fetus. In adults — a marker of liver and germ cell tumors, and a monitoring tool in chronic liver disease.

CA 15-3

Tumor marker used in monitoring breast cancer. Not a screening test — its role is tracking treatment response and recurrence.

CA 19-9

Tumor marker of the pancreas and bile ducts, used for monitoring known disease. Benign biliary conditions raise it too.

HE4 (epididymis protein 4)

A protein used with CA-125 in the ROMA algorithm to estimate the risk of ovarian cancer in women with a pelvic mass.

Carcinoembryonic antigen

A marker used to monitor colorectal and some other cancers. Smoking raises the baseline; not a screening test.

Immunology

ASO (anti-streptolysin O)

Antibodies proving a recent streptococcal infection — used when rheumatic fever or post-streptococcal complications are suspected.

Rheumatoid factor

An antibody supporting the diagnosis of rheumatoid arthritis — informative together with anti-CCP, CRP, and ESR.

Anti-CCP antibodies

The most specific blood marker of rheumatoid arthritis — often positive years before joint symptoms.