The supplement N-ACETYL CYSTEINE (NAC) is increasingly popular among patients suffering from the mental and physical issues NAC claims to improve.

However, the article also states "it is found in most high-protein foods, such as chicken, turkey, yogurt, cheese, eggs, sunflower seeds and legumes".

If a patient wants to know if they are deficient or need to add more:

  • Is there a direct test to measure L-cysteine amino acid levels in the body?

  • If not, is there an indirect test to measure correlated amino acids (such as methionine and serine)?


Measuring the concentration of amino acids "in the body" is a bit difficult. Your body is made up of lots of cells and organs, each one of which exists in a constant state of flux and contains many proteins and amino acids.

Assuming perhaps that you meant "in the blood", then yes, such kits do exist -- e.g. this enzyme-linked spectrophotomeric assay -- https://www.antibodies-online.com/kit/1503021/Cysteine+ELISA+Kit/ -- but it costs €642,85 (+€40 shipping and 22% VAT) for 96 tests, and requires a molecular biology laboratory to use.

The only commonly performed similar tests I am aware of are whole plasma amino acid counts, commonly performed on infants to look for inborn errors of metabolism -- i.e. specific birth defects of metabolism. You can find an example US Hospital page here that contains the reference range for each amino acid.

  • Thanks. Open to any type of test. Looks like the blood test you linked includes that. Guess the question is will the blood test be a good reflection of it, relative to the desired health benefit ? Oct 13 '20 at 4:12
  • 1
    You could do a lot cheaper for the blood test: find an enzyme specific for cysteine which uses i.e. NAD or NADP as another substrate and measure the difference in absorption, Lambert-Beer will give you the concentration. Photometer is 300 USD, enzyme cost may vary
    – Narusan
    Oct 13 '20 at 18:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.