---
title: Biomarker reference ranges
type: index
url: "https://www.test-well.com/biomarkers"
---

# Biomarker reference ranges

> Physician-reviewed reference ranges, interpretation notes and ordering options for every biomarker TestWell measures. Each entry links to a page with sex- and age-specific bands, what high and low values suggest, retest cadence and cited sources.

## Blood Health

- [Basophils](https://www.test-well.com/biomarkers/basophils) — The least common white blood cell, involved in allergic and inflammatory responses.
- [Eosinophils](https://www.test-well.com/biomarkers/eosinophils) — White blood cells involved in allergic responses and parasitic infections.
- [Haptoglobin](https://www.test-well.com/biomarkers/haptoglobin) — A protein that binds free hemoglobin from broken-down red cells. Drops when red cells are being destroyed faster than normal.
- [Hematocrit](https://www.test-well.com/biomarkers/hematocrit) — The percentage of your blood made up of red blood cells.
- [Hemoglobin](https://www.test-well.com/biomarkers/hemoglobin) — The protein in red blood cells that carries oxygen from your lungs to the rest of your body.
- [Lymphocytes](https://www.test-well.com/biomarkers/lymphocytes) — White blood cells central to your immune response, especially against viruses.
- [MCH](https://www.test-well.com/biomarkers/mch) — The average amount of hemoglobin per red blood cell.
- [MCHC](https://www.test-well.com/biomarkers/mchc) — The concentration of hemoglobin within your red blood cells.
- [MCV](https://www.test-well.com/biomarkers/mcv) — The average size of your red blood cells. Helps classify the type of anemia when one is present.
- [Monocytes](https://www.test-well.com/biomarkers/monocytes) — White blood cells that mature into macrophages and clean up debris and pathogens.
- [MPV](https://www.test-well.com/biomarkers/mpv) — The average size of your platelets. Larger platelets are typically younger and more active.
- [Neutrophils](https://www.test-well.com/biomarkers/neutrophils) — The most common type of white blood cell. The first responders to bacterial infection.
- [Platelet Count](https://www.test-well.com/biomarkers/platelet-count) — The cells responsible for blood clotting. Both too few and too many can cause clotting problems.
- [RDW](https://www.test-well.com/biomarkers/rdw) — How much your red blood cells vary in size. Elevations often appear early in nutritional deficiencies.
- [Red Blood Cell Count](https://www.test-well.com/biomarkers/red-blood-cell-count) — The number of oxygen-carrying red cells in your blood.
- [Reticulocyte %](https://www.test-well.com/biomarkers/reticulocyte) — The percentage of red blood cells that are immature (newly produced).
- [Reticulocyte Count](https://www.test-well.com/biomarkers/reticulocyte-count) — Newly formed red blood cells. Reflects how actively your marrow is producing red cells.
- [White Blood Cell Count](https://www.test-well.com/biomarkers/white-blood-cell-count) — The number of infection-fighting cells in your blood. Changes can reflect infection, inflammation, or marrow activity.

## Diabetes & Blood Sugar

- [C-Peptide](https://www.test-well.com/biomarkers/c-peptide) — A byproduct of insulin production. Reflects how much insulin your pancreas is making, not how much you've injected.
- [Fasting Insulin](https://www.test-well.com/biomarkers/fasting-insulin) — How much insulin your pancreas is releasing at rest. High values often indicate insulin resistance.
- [Hemoglobin A1c](https://www.test-well.com/biomarkers/hemoglobin-a1c) — Your average blood sugar over the past 2–3 months. The gold standard for diabetes screening and monitoring.

## Heart Health

- [AFP](https://www.test-well.com/biomarkers/afp) — A protein produced by the fetal liver. Used as a tumor marker in adults and a screening marker in pregnancy.
- [Apolipoprotein B](https://www.test-well.com/biomarkers/apolipoprotein-b) — The protein on every atherogenic lipoprotein particle. A direct count of plaque-forming particles.
- [CA 19-9](https://www.test-well.com/biomarkers/ca-19-9) — A protein elevated in pancreatic and biliary tract cancers. Also rises with benign biliary disease.
- [CA-125](https://www.test-well.com/biomarkers/ca-125) — A protein elevated in many ovarian cancers. Also rises with benign conditions like endometriosis or menstruation.
- [CEA](https://www.test-well.com/biomarkers/cea) — A protein elevated in some cancers. Most often used to monitor colorectal cancer treatment.
- [DHA](https://www.test-well.com/biomarkers/dha) — An omega-3 fatty acid concentrated in the brain and retina. Important for neurological function.
- [EPA](https://www.test-well.com/biomarkers/epa) — An omega-3 fatty acid from fish and algae oils. Has anti-inflammatory and cardiovascular effects.
- [Free PSA %](https://www.test-well.com/biomarkers/free-psa) — The fraction of PSA not bound to other proteins. Helps distinguish benign prostate enlargement from cancer when total PSA is borderline.
- [HDL Cholesterol](https://www.test-well.com/biomarkers/hdl-cholesterol) — The "good" cholesterol — helps remove excess cholesterol from arteries. Higher is generally better.
- [HDL Particle Number](https://www.test-well.com/biomarkers/hdl-particle-number) — The actual count of HDL particles. Higher counts are associated with lower cardiovascular risk.
- [Homocysteine](https://www.test-well.com/biomarkers/homocysteine) — An amino acid that can damage blood vessels at high levels. Tied to B vitamin status (B12, folate, B6).
- [LDL Cholesterol](https://www.test-well.com/biomarkers/ldl-cholesterol) — The "bad" cholesterol that contributes to plaque in arteries. Lower is generally better.
- [LDL Particle Number](https://www.test-well.com/biomarkers/ldl-particle-number) — The actual count of LDL particles. A more direct measure of atherogenic burden than LDL cholesterol.
- [LDL Particle Size](https://www.test-well.com/biomarkers/ldl-particle-size) — The average diameter of your LDL particles. Larger is generally healthier.
- [LDL/HDL Ratio](https://www.test-well.com/biomarkers/ldl-hdl-ratio) — A simple ratio combining LDL and HDL into one risk number. Lower is generally better.
- [Lipoprotein(a)](https://www.test-well.com/biomarkers/lipoprotein-a) — A genetically-determined cholesterol particle that carries independent cardiovascular risk.
- [Non-HDL Cholesterol](https://www.test-well.com/biomarkers/non-hdl-cholesterol) — All your cholesterol minus HDL. Captures every atherogenic particle in one number.
- [NT-proBNP](https://www.test-well.com/biomarkers/nt-probnp) — A hormone fragment released when the heart is stretched. The standard marker of heart-failure status.
- [Omega-3 Index](https://www.test-well.com/biomarkers/omega-3-index) — The percentage of EPA + DHA in your red blood cell membranes. A long-term marker of omega-3 status.
- [PSA Total](https://www.test-well.com/biomarkers/psa-total) — A protein made by the prostate. Screens for prostate inflammation, enlargement, or cancer.
- [Small LDL Particle](https://www.test-well.com/biomarkers/small-ldl-particle) — The count of small, dense LDL particles — the most atherogenic LDL subtype.
- [Total Cholesterol](https://www.test-well.com/biomarkers/total-cholesterol) — The sum of all cholesterol types in your blood. One marker of cardiovascular risk.
- [Triglycerides](https://www.test-well.com/biomarkers/triglycerides) — Fats stored from extra calories. Best measured fasting; influenced heavily by diet and alcohol.
- [VLDL Cholesterol](https://www.test-well.com/biomarkers/vldl-cholesterol) — Very-low-density lipoprotein cholesterol — mostly carries triglycerides. Calculated as triglycerides ÷ 5 in standard panels.

## Hormones

- [Adiponectin](https://www.test-well.com/biomarkers/adiponectin) — A fat-cell hormone with anti-inflammatory and insulin-sensitizing effects. Lower levels are linked to insulin resistance.
- [Aldosterone](https://www.test-well.com/biomarkers/aldosterone) — An adrenal hormone that controls sodium, potassium, and blood pressure.
- [AMH](https://www.test-well.com/biomarkers/amh) — A hormone produced by ovarian follicles. Used as a marker of ovarian reserve in women.
- [Cortisol AM](https://www.test-well.com/biomarkers/cortisol-am) — Your primary stress hormone, naturally highest in the morning. Reflects adrenal gland function.
- [Cortisol PM](https://www.test-well.com/biomarkers/cortisol-pm) — Afternoon cortisol — should be considerably lower than morning levels in a normal diurnal pattern.
- [DHEA-S](https://www.test-well.com/biomarkers/dhea-s) — An adrenal hormone that serves as a precursor for sex hormones. Naturally declines with age.
- [Dihydrotestosterone (DHT)](https://www.test-well.com/biomarkers/dihydrotestosterone-dht) — A potent androgen made from testosterone. Drives male-pattern hair growth and prostate activity.
- [Estradiol](https://www.test-well.com/biomarkers/estradiol) — The primary form of estrogen. Levels vary widely with menstrual cycle, age, and reproductive stage.
- [Free Testosterone](https://www.test-well.com/biomarkers/free-testosterone) — The biologically active, unbound fraction of testosterone. Often more clinically meaningful than total.
- [FSH](https://www.test-well.com/biomarkers/fsh) — A pituitary hormone that drives sex-hormone production. In women it varies dramatically through the menstrual cycle and rises sharply at menopause.
- [IGF-1](https://www.test-well.com/biomarkers/igf-1) — Reflects growth hormone activity. Naturally declines with age.
- [Leptin](https://www.test-well.com/biomarkers/leptin) — A hormone produced by fat cells that signals satiety. Levels generally track body fat percentage.
- [LH](https://www.test-well.com/biomarkers/lh) — A pituitary hormone that triggers ovulation in women and testosterone production in men. Cycle-dependent in women.
- [Progesterone](https://www.test-well.com/biomarkers/progesterone) — A female sex hormone that prepares the uterus for pregnancy. Rises sharply after ovulation.
- [Prolactin](https://www.test-well.com/biomarkers/prolactin) — A pituitary hormone primarily involved in milk production. Also affects menstrual function and fertility.
- [PTH, Intact](https://www.test-well.com/biomarkers/pth-intact) — A hormone that controls calcium balance by acting on bone and kidneys.
- [SHBG](https://www.test-well.com/biomarkers/shbg) — A protein that binds sex hormones. Affects how much testosterone and estrogen are biologically active.
- [Total Testosterone](https://www.test-well.com/biomarkers/total-testosterone) — The total amount of testosterone in circulation, both bound and unbound.

## Inflammation & Autoimmune

- [C-Reactive Protein](https://www.test-well.com/biomarkers/c-reactive-protein) — A general marker of inflammation. The standard CRP test is less sensitive than hs-CRP and is used when active inflammation is suspected.
- [ESR](https://www.test-well.com/biomarkers/esr) — A non-specific marker of inflammation. Slow to rise and slow to fall.
- [hs-CRP](https://www.test-well.com/biomarkers/hs-crp) — A sensitive marker of low-grade inflammation. Used for cardiovascular risk assessment.
- [Rheumatoid Factor](https://www.test-well.com/biomarkers/rheumatoid-factor) — An antibody often present in rheumatoid arthritis. Also seen in other autoimmune and infectious conditions.
- [Total IgA](https://www.test-well.com/biomarkers/total-iga) — An antibody that defends mucosal surfaces (gut, airways). Used to evaluate immune deficiencies and validate other antibody tests.
- [Tryptase](https://www.test-well.com/biomarkers/tryptase) — An enzyme released by mast cells. Used to evaluate mast cell disorders and severe allergic reactions.
- [tTG-IgA](https://www.test-well.com/biomarkers/ttg-iga) — The primary blood test for celiac disease. Looks for antibodies against tissue transglutaminase.

## Iron & Anemia

- [Ferritin](https://www.test-well.com/biomarkers/ferritin) — The protein that stores iron in your body. The single best marker of iron stores.
- [Iron](https://www.test-well.com/biomarkers/iron) — The amount of iron circulating in your blood at the moment. Varies through the day.
- [Iron Saturation](https://www.test-well.com/biomarkers/iron-saturation) — The percentage of your iron-binding capacity currently being used. Iron divided by TIBC.
- [TIBC](https://www.test-well.com/biomarkers/tibc) — The total capacity of your blood proteins to carry iron. Rises when iron is scarce.
- [Transferrin](https://www.test-well.com/biomarkers/transferrin) — The protein that carries iron in the blood. Levels rise when iron stores are low.

## Metabolic Health

- [Activated Partial Thromboplastin Time (aPTT)](https://www.test-well.com/biomarkers/activated-partial-thromboplastin-time-aptt) — How long it takes blood to clot via the intrinsic pathway. Used to monitor heparin therapy and screen for clotting disorders.
- [Albumin](https://www.test-well.com/biomarkers/albumin) — The most abundant protein in blood. Made by the liver; reflects nutrition and liver/kidney health.
- [Albumin/Creatinine Ratio](https://www.test-well.com/biomarkers/albumin-creatinine-ratio) — Urine albumin standardized by urine creatinine. The standard screen for early kidney damage.
- [Alkaline Phosphatase](https://www.test-well.com/biomarkers/alkaline-phosphatase) — An enzyme present in liver, bone, and bile ducts. Used to evaluate liver and bone health.
- [ALT](https://www.test-well.com/biomarkers/alt) — An enzyme found mainly in the liver. Elevations can signal liver cell injury.
- [Amylase](https://www.test-well.com/biomarkers/amylase) — An enzyme made by the pancreas and salivary glands that helps digest carbohydrates.
- [AST](https://www.test-well.com/biomarkers/ast) — An enzyme found in the liver, heart, and muscle. Often interpreted alongside ALT.
- [Bilirubin](https://www.test-well.com/biomarkers/bilirubin) — A yellow pigment made when red blood cells break down. Cleared by the liver.
- [BUN](https://www.test-well.com/biomarkers/bun) — Nitrogen waste from protein metabolism that your kidneys clear. A general kidney-function indicator.
- [Calcium](https://www.test-well.com/biomarkers/calcium) — Most calcium is in bone. Blood levels reflect parathyroid, kidney, and vitamin D function.
- [Carbon Dioxide](https://www.test-well.com/biomarkers/carbon-dioxide) — Mostly bicarbonate. Reflects your body's acid-base balance.
- [Chloride](https://www.test-well.com/biomarkers/chloride) — An electrolyte that helps maintain fluid balance and acid-base status.
- [Copper](https://www.test-well.com/biomarkers/copper) — A trace mineral essential for iron metabolism, energy production, and connective tissue health.
- [Creatine Kinase](https://www.test-well.com/biomarkers/creatine-kinase) — An enzyme released when muscle is damaged — skeletal, cardiac, or smooth muscle.
- [Creatinine](https://www.test-well.com/biomarkers/creatinine) — A waste product cleared by your kidneys. Levels reflect how well your kidneys are filtering.
- [Cystatin C](https://www.test-well.com/biomarkers/cystatin-c) — A small protein cleared by the kidneys. An alternative kidney-function marker, especially useful when muscle mass is unusual.
- [D-Dimer](https://www.test-well.com/biomarkers/d-dimer) — A fragment from broken-down clots. Used to rule out clotting disorders like DVT or pulmonary embolism.
- [Direct Bilirubin](https://www.test-well.com/biomarkers/direct-bilirubin) — The processed (conjugated) form of bilirubin that the liver has prepared for excretion.
- [eGFR](https://www.test-well.com/biomarkers/egfr) — An estimate of how much blood your kidneys filter per minute, calculated from creatinine.
- [eGFR (Cystatin C)](https://www.test-well.com/biomarkers/egfr-cystatin-c) — Estimated kidney filtration rate calculated from cystatin C. Often used to confirm creatinine-based eGFR.
- [Fibrinogen](https://www.test-well.com/biomarkers/fibrinogen) — A clotting protein. Also rises with inflammation as an acute-phase reactant.
- [GGT](https://www.test-well.com/biomarkers/ggt) — A liver enzyme that's especially sensitive to bile-flow problems and alcohol-related liver stress.
- [Glucose](https://www.test-well.com/biomarkers/glucose) — Your blood sugar level. Fasting glucose is one of the primary screens for diabetes.
- [INR](https://www.test-well.com/biomarkers/inr) — A standardized version of prothrombin time. Lets PT results be compared across labs and methods.
- [LDH](https://www.test-well.com/biomarkers/ldh) — An enzyme released when cells are damaged. Non-specific — many tissues contain it.
- [Lead (Blood)](https://www.test-well.com/biomarkers/lead-blood) — Lead level in the blood. The CDC reference value for adults is <3.5 mcg/dL; any detectable level is a concern over time.
- [Lipase](https://www.test-well.com/biomarkers/lipase) — An enzyme made by the pancreas that helps digest fats. More specific to the pancreas than amylase.
- [Magnesium](https://www.test-well.com/biomarkers/magnesium) — A mineral involved in 300+ enzyme reactions, including muscle, nerve, and heart function.
- [Mercury (Blood)](https://www.test-well.com/biomarkers/mercury-blood) — Blood mercury level. Mostly reflects recent exposure (commonly from fish consumption).
- [Phosphorus](https://www.test-well.com/biomarkers/phosphorus) — A mineral that, with calcium, builds bones and teeth and supports many cellular processes.
- [Potassium](https://www.test-well.com/biomarkers/potassium) — An electrolyte essential for heart, muscle, and nerve function.
- [Prealbumin](https://www.test-well.com/biomarkers/prealbumin) — A protein with a short half-life — drops quickly when nutrition is inadequate. A sensitive nutrition marker.
- [Prothrombin Time](https://www.test-well.com/biomarkers/prothrombin-time) — How long it takes blood to clot via the extrinsic pathway. Used to monitor warfarin therapy.
- [Selenium](https://www.test-well.com/biomarkers/selenium) — An antioxidant trace mineral important for thyroid function and immune health.
- [Sodium](https://www.test-well.com/biomarkers/sodium) — A key electrolyte that controls fluid balance, blood pressure, and nerve and muscle function.
- [Total Protein](https://www.test-well.com/biomarkers/total-protein) — The total of albumin and globulins in your blood. A general nutrition and liver/kidney indicator.
- [Uric Acid](https://www.test-well.com/biomarkers/uric-acid) — A waste product from nucleic-acid breakdown. High levels can crystallize in joints and cause gout.
- [Urine Albumin](https://www.test-well.com/biomarkers/urine-albumin) — A small amount of albumin in the urine. Early sign of kidney damage from diabetes or hypertension.
- [Urine Creatinine](https://www.test-well.com/biomarkers/urine-creatinine) — A measure used to standardize other urine tests (like albumin) for hydration level.
- [Zinc](https://www.test-well.com/biomarkers/zinc) — An essential trace mineral important for immune function, wound healing, and taste/smell.

## Thyroid

- [Free T3](https://www.test-well.com/biomarkers/free-t3) — The active, unbound form of T3 — the most metabolically active thyroid hormone.
- [Free T4](https://www.test-well.com/biomarkers/free-t4) — The active, unbound form of the main thyroid hormone. Confirms thyroid function alongside TSH.
- [Reverse T3](https://www.test-well.com/biomarkers/reverse-t3) — An inactive form of T3 that the body produces during stress, illness, or low-calorie states.
- [Thyroglobulin Antibodies](https://www.test-well.com/biomarkers/thyroglobulin-antibodies) — Antibodies against thyroglobulin. Often elevated in Hashimoto's thyroiditis alongside TPO antibodies.
- [TPO Antibodies](https://www.test-well.com/biomarkers/tpo-antibodies) — Antibodies against thyroid peroxidase. The most common marker of autoimmune thyroid disease.
- [TSH](https://www.test-well.com/biomarkers/tsh) — A pituitary hormone that signals your thyroid. The most sensitive screen for thyroid problems.

## Vitamins & Nutrients

- [Folate](https://www.test-well.com/biomarkers/folate) — A B vitamin essential for DNA synthesis and red blood cell formation.
- [Methylmalonic Acid](https://www.test-well.com/biomarkers/methylmalonic-acid) — A metabolite that builds up when cells lack usable vitamin B12. The most specific marker of functional B12 deficiency.
- [Vitamin A (Retinol)](https://www.test-well.com/biomarkers/vitamin-a-retinol) — A fat-soluble vitamin essential for vision, immune function, and skin health.
- [Vitamin B1 (Thiamine)](https://www.test-well.com/biomarkers/vitamin-b1-thiamine) — A B vitamin essential for energy metabolism and nerve function.
- [Vitamin B12](https://www.test-well.com/biomarkers/vitamin-b12) — A vitamin essential for nerve function and red blood cell formation. Found in animal foods.
- [Vitamin B2 (Riboflavin)](https://www.test-well.com/biomarkers/vitamin-b2-riboflavin) — A B vitamin needed for energy production and red blood cell formation.
- [Vitamin B6](https://www.test-well.com/biomarkers/vitamin-b6) — A B vitamin involved in protein metabolism, neurotransmitter synthesis, and immune function.
- [Vitamin C](https://www.test-well.com/biomarkers/vitamin-c) — A water-soluble antioxidant essential for collagen synthesis and immune function.
- [Vitamin D, 25-Hydroxy](https://www.test-well.com/biomarkers/vitamin-d-25-hydroxy) — Your body's vitamin D status. Influenced by sun exposure, diet, supplements, and absorption.
- [Vitamin E](https://www.test-well.com/biomarkers/vitamin-e) — A fat-soluble antioxidant that protects cell membranes from damage.
- [Vitamin K1](https://www.test-well.com/biomarkers/vitamin-k1) — A fat-soluble vitamin essential for blood clotting and bone health.

---

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