MTHFR gene test
Blood test for two common variants in the MTHFR gene, which is involved in folate metabolism
Also known as
Definition
The MTHFR gene test checks a blood sample for the two most common variants in the MTHFR gene, C677T and A1298C. The gene carries the instructions for the enzyme methylenetetrahydrofolate reductase, which helps the body use folate. Folate and other B vitamins are needed to break down the amino acid homocysteine. Every person carries two copies of the gene, one from each parent.
| Parameter | Value |
|---|---|
| Unit | no measured value; result reported as genotype (negative or positive) |
| Reference Range | No reference range in the usual sense: the result is negative (neither of the two common variants C677T and A1298C found) or positive, stating which variant is present in one or both gene copies. Presentation and wording differ between labs; your own report is what counts. Your doctor puts the result in context. |
Agree on your personal target range with your doctor.
↓ What a low value means
The test does not give a low or high value but a negative or positive result. Negative means that neither of the two common variants was found. If homocysteine is still raised, MedlinePlus says another cause is likely, such as a lack of B vitamins, certain medicines, older age, an underactive thyroid or kidney disease. This test does not detect rare MTHFR variants; other gene tests are used to look for them. Your doctor puts the result in context.
↑ What a high value means
Positive means that at least one of the two variants was found in one or both gene copies. These variants are common; according to the CDC, more people in the United States carry one or two copies of C677T than carry none. A variant in only one gene copy is unlikely to cause health problems, and a positive result guarantees neither a higher risk of disease nor raised homocysteine. If homocysteine is raised, MedlinePlus says two copies of C677T or one copy each of C677T and A1298C are probably involved, whereas two copies of A1298C probably are not. Discuss the result with your doctor.
When to test
Experts do not recommend testing for the common variants in most cases. It is sometimes ordered when homocysteine is raised and, in addition, a close relative carries an MTHFR variant or early heart or blood vessel disease has occurred in the family. Other reasons are planned treatment with methotrexate, where the result can help with choosing the dose, and an abnormal newborn screening result for homocystinuria. No preparation is needed.
Frequently asked questions
Why is the MTHFR test often not recommended? +
According to MedlinePlus, treatment of raised homocysteine is the same whether or not one of the two common variants is the cause. It is also unclear whether homocysteine itself affects the risk of blood clots or early heart and blood vessel disease. Some experts therefore advise against using the test for this purpose.
What does the MTHFR gene have to do with homocysteine? +
The MTHFR enzyme helps the body use folate, which together with other B vitamins breaks down homocysteine. If a variant makes the enzyme work less well, homocysteine levels can rise. It is not certain whether raised homocysteine itself causes health problems; some studies show it can damage the inner lining of blood vessels, which may increase the risk of blood clots, heart disease and stroke.
Can people with an MTHFR variant use folic acid? +
Yes. The US public health agency CDC states that people with an MTHFR variant can process all types of folate, including folic acid. At the same folic acid intake, people with two copies of C677T have on average only about 16 % lower blood folate than people without this variant; according to the CDC, intake matters more for blood folate than genotype. Discuss questions about diet or supplements with your doctor.
How does this differ from homocystinuria? +
Homocystinuria is a rare inherited disease that can lead to very high homocysteine levels. Symptoms usually appear in the first year of life, in mild cases only in childhood or later. It can be caused by rare MTHFR variants, which are looked for with different gene tests than C677T and A1298C.
MTHFR gene test
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.