Vitamin A Blood Test: Normal Levels, Deficiency & Toxicity

The vitamin A (retinol) blood test measures a fat-soluble vitamin your liver stores. Learn normal levels, signs of deficiency (night blindness), and why too much can be toxic.

Published July 20, 202610 min readWritten by the Blood Analysis Team · Reviewed and verified by Julien Priour

Vitamin A (also called retinol) is a fat-soluble vitamin essential for vision, immunity, skin and mucous membranes, and reproduction. Your body stores it in the liver and measures it in the blood as serum retinol. This guide covers normal vitamin A levels, what a low result (deficiency) or a high result (toxicity) means, why vitamin A is one of the few vitamins that can become dangerous in excess, and why the test needs careful interpretation. Vitamin A is best read alongside your other fat-soluble vitamins in a broader vitamin panel, with vitamin D and B12.

Key takeaways

Vitamin A (retinol) is a fat-soluble vitamin stored in the liver, essential for night vision, immunity, skin/mucous membranes, and reproduction.¹²
It is measured as serum retinol; an indicative adult range is ~1.05–2.80 µmol/L (≈30–80 µg/dL), with deficiency defined as retinol < 0.70 µmol/L (< 20 µg/dL) — values vary by lab.³⁴
Deficiency causes night blindness and then xerophthalmia (dry eye, Bitot's spots, keratomalacia): it is the leading cause of preventable childhood blindness worldwide and weakens immunity.⁴⁵
⚠️ Vitamin A can be toxic in excess (hypervitaminosis A): high-dose supplements or liver/organ meats can cause headache, nausea, liver injury, raised intracranial pressure, and bone problems.⁶¹
⚠️ In high doses vitamin A is teratogenic: avoid high-dose vitamin A and retinoids (isotretinoin) before and during pregnancy.⁷¹
Serum retinol poorly reflects body stores (they are tightly regulated) except in marked deficiency or excess, and it falls during inflammation — it is not a cancer marker.³

What is vitamin A (retinol)?

Vitamin A is a family of fat-soluble compounds called retinoids, whose main circulating form is retinol. Your diet supplies it in two forms:¹²

preformed vitamin A (retinol and retinyl esters), from animal foods: liver and organ meats, dairy, egg yolk, oily fish;
provitamin A carotenoids, including beta-carotene, from plant foods: carrots, sweet potato, leafy greens, orange fruits. The body converts these into vitamin A as needed.⁸

Once absorbed, vitamin A is stored in the liver, which releases just what the body needs into the blood, carried by retinol-binding protein (RBP). Vitamin A is essential for vision — it forms rhodopsin, the retinal pigment needed to see in dim light — as well as for the turnover of skin and mucous membranes, the immune response, and reproduction and fetal development.²⁴

Retinol is not beta-carotene. Preformed retinol can become toxic in excess; the beta-carotene in vegetables does not cause classic toxicity (at most a harmless orange tint to the skin). That distinction matters, as you'll see below.

Why the test is done

The serum retinol test is not a routine screen. Your clinician may order it in targeted situations:³⁴

suspected deficiency: trouble seeing in dim light, dry eyes, frequent infections — especially in children;
fat-malabsorption conditions, because vitamin A is fat-soluble: cystic fibrosis, cholestasis and liver/bile-duct disease, celiac disease, inflammatory bowel disease, and after bariatric (weight-loss) surgery;⁶
severe malnutrition or very restrictive diets;
suspected overdose (hypervitaminosis A) from prolonged supplement use or heavy liver consumption.

Outside these indications, the result adds little. It is not a general screening test and not a cancer marker. In low-income settings, vitamin A status is assessed mainly as a public-health measure.⁵

How the test is done

The vitamin A test is a standard blood draw from a vein. It usually does not require fasting, though some labs advise it — especially when the test is run with a lipid panel or other fat-soluble vitamins. The sample is light-sensitive (retinol degrades in light) and must be protected. Always follow the exact instructions on your order (see fasting before a blood test).³

Normal ranges

Below are indicative adult reference values for serum retinol. They vary by lab, age, and assay method — always compare against the range printed on your report.

Status	Serum retinol (SI)	Conventional unit
Deficiency (WHO definition)	< 0.70 µmol/L	< 20 µg/dL
Normal adult range (indicative)	~1.05 – 2.80 µmol/L	~30 – 80 µg/dL
Possible excess (check against retinyl esters)	> ~3.5 µmol/L	> ~100 µg/dL

Units: to convert, µg/dL × 0.0349 = µmol/L. One key caveat: serum retinol poorly reflects the liver's stores, because the body keeps it stable until reserves run very low; it also falls during inflammation (RBP is a negative acute-phase protein), so it is best read alongside CRP. Conversely, toxicity shows up mainly as raised retinyl esters, not necessarily retinol alone. Only your clinician can interpret the number in your context.³

Understanding your results

Low vitamin A (deficiency)

A low vitamin A means deficiency, and its earliest effects are in the eye. The first sign is night blindness (difficulty seeing in dim light), because retinol is essential for rhodopsin. Left uncorrected, deficiency progresses to xerophthalmia: drying of the conjunctiva and cornea, Bitot's spots, then keratomalacia (softening of the cornea) that can cause permanent blindness. Vitamin A deficiency is the leading cause of preventable childhood blindness worldwide and also weakens immunity, worsening infections such as diarrhea and measles.⁴⁵

Common causes of a low retinol:³⁶

inadequate intake (malnutrition, very restrictive diets, poverty) — the dominant cause globally;
fat malabsorption: cystic fibrosis, cholestasis and hepatobiliary disease (see liver function tests), celiac disease, inflammatory bowel disease, and bariatric surgery;
ongoing inflammation or infection, which artificially lowers retinol without necessarily reflecting true depleted stores — hence reading it together with CRP.

High vitamin A (toxicity)

Unlike water-soluble vitamins, fat-soluble vitamin A accumulates, so an excess can become toxic (hypervitaminosis A). It almost always comes from high-dose supplements or heavy intake of liver/organ meats (very rich in retinol) — never from the beta-carotene in vegetables. Signs of toxicity can include headache, nausea, dry skin, hair loss, bone pain and bone fragility, liver injury, and, in marked cases, raised intracranial pressure (headache, visual disturbance). In children treated for a malabsorption disorder, over-supplementation can even cause hypercalcemia.⁶¹

Vitamin A and pregnancy: a critical message. In high doses, vitamin A is teratogenic: large studies have linked a high intake of preformed vitamin A (above roughly 10,000 IU/day from supplements) to an increased risk of birth defects. That is why you should avoid high-dose vitamin A and retinoids — such as isotretinoin, an acne derivative — before and during pregnancy.⁷¹ Any supplementation, its dose, and its duration should be decided with your clinician.

Vitamin A and cancer? Retinol is not a cancer marker, and a high or low value does not "screen" for any tumor. Beware a common mix-up: at high doses, beta-carotene supplements actually increased lung cancer risk in heavy smokers in two large trials (ATBC and CARET) — but that concerns high-dose supplements in smokers, not vitamin A from a balanced diet.⁹¹⁰

What affects your vitamin A

Many factors change serum retinol: dietary intake (liver, dairy, eggs, beta-carotene-rich vegetables), fat absorption (so the health of your liver, bile ducts, pancreas, and gut), supplements or retinoid medications, ongoing inflammation/infection (which lowers retinol via RBP), zinc status (needed to mobilize vitamin A), and — for the draw itself — light exposure of the sample. Tell your clinician about your supplements, medications (including vitamin A derivatives), and diet: they all change the interpretation.³¹

Recent research

According to recent PubMed-indexed publications:

Supplementing children saves lives where deficiency is common. A Cochrane review (47 studies, ~1.2 million children) confirms that vitamin A supplementation in children aged 6 months to 5 years cuts all-cause mortality by about 12% and clearly reduces the incidence of diarrhea, measles, night blindness, and Bitot's spots — supporting the WHO programs in at-risk populations.¹¹ (Imdad A et al., Cochrane Database Syst Rev, 2022 — DOI.)
Deficiency is the top cause of preventable childhood blindness. An epidemiological review notes that vitamin A deficiency remains a major public-health problem, driving xerophthalmia and excess deaths from infection, with prevalence falling thanks to supplementation and food fortification.⁴
High-dose supplements can harm. In contrast to deficiency settings, excess vitamin A can be harmful: at high doses, beta-carotene supplements increased lung cancer in smokers (the ATBC and CARET trials), and a high intake of preformed vitamin A is teratogenic in pregnancy.⁹¹⁰⁷
Measuring true status is hard. Biomarker work (the BOND project) stresses that serum retinol is homeostatically controlled and only drops when liver reserves are low, so other methods (isotope dilution, retinyl ester measurement) are needed to gauge both deficiency and excess.³

These findings concern diagnosis and research; they do not authorize self-medication and do not replace your physician's advice.

Get your vitamin A interpreted by AI DiagMe

A retinol level is never read alone: its meaning depends on your diet, your fat absorption (liver, bile ducts, gut), any inflammation (read against CRP), your supplements, and your context — including pregnancy. That cross-reading is what gives the result its real value.

👉 AI DiagMe interprets your lab results — blood, urine, or stool — in plain language, taking your whole profile into account. An informational service that does not provide a diagnosis and complements, never replaces, your physician.

Frequently asked questions

What does vitamin A (retinol) do?

It's a fat-soluble vitamin essential for vision (especially in dim light), immunity, the turnover of skin and mucous membranes, and reproduction. The body stores it in the liver and draws on it as needed.

What is a normal vitamin A level?

Indicatively, a serum retinol of ~1.05–2.80 µmol/L (≈30–80 µg/dL) in adults, with deficiency defined as < 0.70 µmol/L (< 20 µg/dL). Values vary by lab, so read the range on your report.

What are the signs of vitamin A deficiency?

The earliest sign is night blindness. Uncorrected, it leads to dry eyes, Bitot's spots, and corneal damage that can cause blindness. Deficiency also weakens immunity. It occurs mainly with malnutrition or fat malabsorption.

Can vitamin A be dangerous in excess?

Yes. Because it is fat-soluble, it accumulates. An excess (high-dose supplements, liver/organ meats) can cause headache, nausea, liver injury, raised intracranial pressure, and bone fragility. It is one of the few vitamins whose overdose is genuinely toxic.

Vitamin A and pregnancy: what's the risk?

In high doses, vitamin A is teratogenic (risk of birth defects). Avoid high-dose vitamin A and retinoids (such as isotretinoin for acne) before and during pregnancy. Dietary beta-carotene does not carry this risk. Discuss it with your clinician.

Do I need to fast for a vitamin A test?

Usually no, but some labs advise it, especially when the test accompanies a lipid panel. Follow the instructions on your order.

Beta-carotene and cancer — should I worry?

Beta-carotene from food is safe. It was high-dose supplements that, in heavy smokers, increased lung cancer in two large trials. Vitamin A from a balanced diet is not a cancer marker or cause.

How is vitamin A deficiency corrected?

By treating the cause (improving diet, managing malabsorption) and, if needed, with supplementation whose dose your clinician sets — all the more so because excess is toxic. Don't supplement blindly.

Bottom line

Vitamin A (retinol) is a fat-soluble vitamin stored in the liver, essential for vision, immunity, skin, and reproduction. Keep the ballpark in mind (~1.05–2.80 µmol/L, deficiency < 0.70 µmol/L, lab-dependent), remember that deficiency causes night blindness then xerophthalmia (the leading cause of preventable childhood blindness), and — unlike water-soluble vitamins — that its excess is toxic and teratogenic in pregnancy. Serum retinol poorly reflects body stores and falls during inflammation; it is not a cancer marker. No value is read alone — it's your whole set of markers and your context that counts, which is what AI DiagMe provides, alongside your physician.

Sources

Official U.S./international sources and peer-reviewed publications (PubMed) used for this guide:

NIH Office of Dietary Supplements — Vitamin A and Carotenoids: Fact Sheet for Health Professionals. ods.od.nih.gov ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷
Cleveland Clinic — Vitamin A. my.clevelandclinic.org ↩ ↩² ↩³
Tanumihardjo SA, Russell RM, Stephensen CB, et al. Biomarkers of Nutrition for Development (BOND)—Vitamin A Review. J Nutr, 2016. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸
Sherwin JC, Reacher MH, Dean WH, Ngondi J. Epidemiology of vitamin A deficiency and xerophthalmia in at-risk populations. Trans R Soc Trop Med Hyg, 2012. PubMed · DOI ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶
World Health Organization — Vitamin A deficiency and supplementation in infants and children. who.int ↩ ↩² ↩³
Safi KH, Filbrun AG, Nasr SZ. Hypervitaminosis A causing hypercalcemia in cystic fibrosis. Case report and focused review. Ann Am Thorac Soc, 2014. PubMed · DOI ↩ ↩² ↩³ ↩⁴
Rothman KJ, Moore LL, Singer MR, et al. Teratogenicity of high vitamin A intake. N Engl J Med, 1995. PubMed · DOI ↩ ↩² ↩³
MedlinePlus (U.S. National Library of Medicine, NIH) — Vitamin A. medlineplus.gov ↩
Albanes D, Heinonen OP, Taylor PR, et al. Alpha-Tocopherol and beta-carotene supplements and lung cancer incidence in the ATBC Study. J Natl Cancer Inst, 1996. PubMed · DOI ↩ ↩²
Goralczyk R. Beta-carotene and lung cancer in smokers: review of hypotheses and status of research. Nutr Cancer, 2009. PubMed · DOI ↩ ↩²
Imdad A, Mayo-Wilson E, Haykal MR, et al. Vitamin A supplementation for preventing morbidity and mortality in children from six months to five years of age. Cochrane Database Syst Rev, 2022. PubMed · DOI ↩