What is an MTHFR gene test?

An MTHFR gene test checks a sample of your blood for two very common changes in a gene called MTHFR. Changes in your genes are also called gene variants or mutations.

Genes are parts of DNA in your cells that you inherit from your parents. You inherit two copies of each gene, one coming from each parent. Genes carry information that controls what you look like and how your body works.

The MTHFR gene provides instructions for making the MTHFR protein. This protein helps your body use folate, a type of B vitamin that you get from various foods. Normally, your body uses folate and other B vitamins to break down an amino acid called homocysteine. Because of this, only small amounts of homocysteine stay in your bloodstream. If you have a change in the MTHFR gene, however, the MTHFR protein may not process folate as well as it should. As a result, you may have increased levels of homocysteine in your blood.

In general, medical researchers aren't certain that increased homocysteine levels directly cause health problems. However, some studies have shown that they can damage the inside of your blood vessels. This may increase the risk for blood clots, heart disease, and stroke.

Higher homocysteine levels during pregnancy can also increase the risk of having:

• A baby with neural tube defects.
• Early pregnancy loss (a miscarriage).
• Preeclampsia.

To lower homocysteine levels, your health care provider will usually recommend taking vitamin B supplements that include folic acid, which is a form of folate.

However, if you have the gene variant MTHFR, your provider may recommend methylfolate (5-MTHF) instead since your body may be able to use this form more easily. The extra vitamins can make up for an MTHFR gene that's not fully working. Your provider may recommend eating more foods with folate, too. Before making changes in your health habits, talk with your provider.

Studies show that taking folic acid greatly reduces the risk of neural tube defects in babies. So, even if you have the MTHFR gene variant, the U.S. Centers for Disease Control and Prevention (CDC) recommends folic acid supplements for everyone who may become pregnant.

Other names: methylenetetrahydrofolate reductase mutation, C677T and A1298C, MTHFR DNA assay, MTHFR DNA testing, MTHFR gene variants, MTHFR gene polymorphisms 677T>C & 1298A>C mutations

What is it used for?

An MTHFR gene test looks for the two most common MTHFR gene variants. These are called C677T and A1298C. It can be done alone or as part of a group of genetic tests.

Having either of these variants does not necessarily increase your risk for any health condition. Nor does it guarantee that you will have high homocysteine levels. So, your health care provider may only check for these variants if a homocysteine blood test has already shown that your homocysteine levels are high.

If a homocysteine blood test does show high homocysteine levels, an MTHFR test can:

• Determine whether the C667T and/or A1298C variants are causing these high levels.
• Estimate your risk of developing blood clots or early heart or blood vessel disease, especially if you have a family history of these conditions.

However, even if a homocysteine blood test shows that your homocysteine levels are higher than normal, an MTHFR gene test is generally not needed. That's because:

• The treatment for high homocysteine levels is the same whether or not it's caused by one of the two most common variants of the MTHFR gene.
• Researchers aren't certain whether homocysteine levels affect your risk for developing blood clots or early heart or blood vessel disease. Because of this, some medical experts recommend against using MTHFR testing for this purpose.

To lower homocysteine levels, your provider will usually recommend taking vitamin B supplements that include folic acid, which is a form of folate. However, if you have the gene variant MTHFR, your provider may recommend methylfolate (5-MTHF) instead since your body may be able to use this form more easily. The extra vitamins can make up for an MTHFR gene that's not fully working.

Your provider may also order MTHFR testing if a newborn has a positive result in a routine homocystinuria screening test. Most newborns in the U.S. receive this screening shortly after birth.

Why do I need an MTHFR gene test?

Medical experts do not recommend testing for common MTHFR gene changes in most cases. However, your provider may order this test if you had a blood test that showed higher than normal levels of homocysteine and:

• A close relative was diagnosed with an MTHFR gene change.
• You and/or close family members have early heart or blood vessel disease.

You may also need an MTHFR gene test if your provider prescribes a medicine called methotrexate. Methotrexate is used to treat certain types of cancer, psoriasis, and rheumatoid arthritis. The MTHFR protein helps your body use this medicine properly. The results of a MTHFR gene test may help your provider choose the dose that will be safe for you.

What happens during an MTHFR gene test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for an MTHFR gene test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

The results of an MTHFR gene test tell you whether you have one or both of the two most common changes in the MTHFR gene. Test results are usually reported as positive or negative:

• A positive test result means that you have an MTHFR gene change in one or both of your MTHFR genes. Having a change in only one of your MTHFR genes is unlikely to cause any health problems. If your homocysteine levels are high and your MTHFR gene test shows that you have:
• Two copies of the C677T gene change or one copy each of C677T and A1298C, then these gene changes are probably causing your increased homocysteine levels
• Two copies of the A1298C gene change, then your increased homocysteine levels are probably not caused by these gene changes
• A negative test result means that neither of the common MTHFR gene changes were found in your blood sample. If you have an increased homocysteine level, it's probably from another condition, such as a lack of B vitamins, taking certain medicines, older age, hypothyroidism, kidney disease, or another disease.

If you have questions about your results, talk with your provider.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about an MTHFR gene test?

Different types of gene tests are used to look for rare types of MTHFR gene changes that can cause a genetic disease called homocystinuria. This disease prevents your body from making an enzyme (a protein that speeds up chemical reactions in your body) that helps break down homocysteine. It can cause very high homocysteine levels. Symptoms usually show up in the first year of life. In mild cases, symptoms may not appear until childhood or later.