Testing for Vitamin A Poisoning – Serum Retinol

by Oct 27, 2023BLOG, ENGLISH1 comment

laboratory test

Serum retinol is one of the most common vitamin A tests but also one of the least useful.

Serum retinol levels can not be used to either diagnose or dismiss vitamin A poisoning.

Your serum retinol levels can be above or BELOW normal or it can be normal and yet you can still be vitamin A poisoned.

Here are the documents that support this view:

1. “Liver Damage Caused by Therapeutic Vitamin A Administration: Estimate of Dose-Related Toxicity in 41 Cases”

This study involved 41 patients. All patients were confirmed to be vitamin A poisoned based on liver biopsies.

24 of the 41 had their serum retinol tested.

Of those 24:

  • 4 were below normal
  • 11 were normal
  • 9 were above normal

Normal range for serum retinol was 25 to 75 mcg/dl.

Conclusion:  Serum retinol can not be used to confirm vitamin A poisoning.

Source: https://www.gastrojournal.org/article/0016-5085(91)90672-8/pdf

2. “Vitamin A toxicity: When one a day doesn’t keep the doctor away”

This is a case report of a man who had confirmed vitamin A poisoning based on a liver biopsy but had normal retinol levels:

The patient’s free retinol level was normal.

Source: https://aasldpubs.onlinelibrary.wiley.com/doi/10.1002/lt.21007

3. “Hepatic Injury from Chronic Hypervitaminosis a Resulting in Portal Hypertension and Ascites”


This is another case report of a woman with vitamin A toxicity as confirmed via liver biopsy.

“The serum vitamin A level was slightly elevated at 58.7 ug per 100 ml (normal, 30 to 50)”.

Although it was elevated based on a reference range of 30 to 50 mcg/dl, the result is within a normal range if a reference range of maximum 75 mcg/dl from the previous paper are applied.

Source: https://www.nejm.org/doi/full/10.1056/NEJM197408292910903

4. Merck Manual


The Merck Manuals published by the pharmaceutical company Merck & Co are as mainstream medicine as you can go.

They are used as an authoritative source of medical information.

Here is what they say about diagnosing vitamin A toxicity:

“Diagnosis of vitamin A toxicity is clinical. Blood vitamin levels correlate poorly with toxicity. However, if clinical diagnosis is equivocal, laboratory testing may help. In vitamin A toxicity, fasting serum retinol levels may increase from normal (28 to 86 mcg/dL [1 to 3 mcmol/L]) to > 100 mcg/dL (> 3.49 mcmol/L), sometimes to > 2000 mcg/dL (> 69.8 mcmol/L). Hypercalcemia is common.

Differentiating vitamin A toxicity from other disorders may be difficult. Carotenosis may also occur in severe hypothyroidism and anorexia nervosa, possibly because carotene is converted to vitamin A more slowly.”

Source: https://www.merckmanuals.com/professional/nutritional-disorders/vitamin-deficiency,-dependency,-and-toxicity/vitamin-a-toxicity

5. “Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc”


This document issued by the National Academy of Sciences on dietary reference intakes is part of an “authoritative series” with recommendation on vitamin and mineral intakes.

Here is what they say about serum retinol testing:

“Because of the relatively insensitive relationship between plasma retinol concentration and liver vitamin A in the adequate range, and because of the potential for confounding factors to affect the level and interpretation of the concentration, it was not chosen as a primary status indicator for a population for estimating an average requirement for vitamin A.”

Translation into English: There is no relationship between the liver stores of vitamin A and plasma retinol. The liver stores determine the real vitamin A burden. Serum retinol can not reflect those adequately.

Source: https://nap.nationalacademies.org/read/10026/chapter/6#102

6. “The acute and chronic toxic effects of vitamin A”


This is a document authored by researchers from the Department of Nutritional Sciences, University of Wisconsin-Madison.

It also appears to be of some authoritative value for conventional medicine, since it’s used as a source by Wikipedia.

A quote from the paper about serum retinol:

“Assessing vitamin A status in persons with subtoxicity or toxicity is complicated because serum retinol concentrations are nonsensitive indicators in this range of liver vitamin A reserves.”

Source: https://pubmed.ncbi.nlm.nih.gov/16469975/

No standardized reference levels for serum retinol


Another problem with serum retinol is that there are no universally agreed upon reference ranges for what is normal or not, as one can see based on the above examples.

What is considered normal can differ from one laboratory to the next and from one scientific paper to another.

One of the above documents used a reference range of 30 to 50 mcg/dl as normal.

The other went up to 75 mcg/dl.

Yet other sources go even higher up to 120 mcg/dl.

The first laboratory I used in Germany cites the normal range as being 30 to 60 mcg/dl.

A laboratory I used in a different country cited values of 30 to 70 mcg/dl.

The Livertox database, set up by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), cites 37 to 45 mcg/dl as normal for an 18-year-old person, or 30 to 50 mcg/dl for a 63 years old.

The University of California says it’s 15 to 60 mcg/dl.

Depending on what laboratory you use and depending on what source you consult, your serum retinol levels can be considered deficient, normal, or toxic.

Serum retinol as a tracking tool


I believe the serum retinol is still a useful tool, but no so much to diagnose vitamin A poisoning, but instead to track one’s progress on a vitamin A deficient diet, especially to track the detox setback phase.

The setback is a phase that sets in after around 2 to 3 months on a low vitamin A diet. According to Grand Genereux and Dr. Garrett Smith this can be observed in around 50% of the cases.

During that phase, one can experience a reversal of previous gains. New symptoms can appear as well, or old ones from years ago that seemed to be long gone.

During this detox setback, serum retinol levels tend to go up.

Once the setback is overcome, serum retinol comes back down again.

You can see this on my serum retinol results of the past 15 months:

This graph tracks my serum retinol levels from December 2021 until December 2022. During that time I followed a strict vitamin A deficient diet of mostly beef and black beans, with some occasional rice (less than 100 IU of vitamin A per day). I was testing my serum retinol every month, except in January 2022 and in the period between February and June 2022, hence the missing results. But even with the incomplete data, one can see clearly the detox setback phase. It likely started sometime in February 2022 (around 3  months after the beginning of my low vit A experiment). This coincided with a regression of some of my symptoms and the emergence of new ones.


Note, October 27th, 2023: This is an article that I originally published on my vitaminapoisoning.com website (now deleted).


1 Comment
  1. Susan Stewart

    Thanks for this, Paola.


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