What is an MTHFR gene test?

A MTHFR gene test uses a sample of your blood to look for two very common changes in a gene called MTHFR. A change in this gene is also called an MTHFR variant or MTHFR mutation. Genes are parts of DNA in your cells that you inherit from your parents. Genes carry information that controls what you look like and how your body works.

You have two copies of the MTHFR gene, one from each parent. The genes provide instructions for making the MTHFR protein. This protein helps your body use folate, a type of B vitamin that you get from many foods. Your body needs folate and other B vitamins to break down an amino acid called homocysteine.

Normally, your body quickly breaks down homocysteine, so you have very little in your bloodstream. But if you have a change in an MTHFR gene, the MTHFR proteins your body makes may not process folate as well as they should. As a result, you may have increased levels of homocysteine in your blood.

In general, researchers aren't certain that increased homocysteine levels directly cause health problems. But some studies have linked too much homocysteine to damage to the inside of your blood vessels. This may increase the risk for blood clots, heart disease, and stroke. Also, the risk of having a baby with neural tube defects is slightly higher if homocysteine levels are high during pregnancy.

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 a common change in your MTHFR gene.

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. Folic acid may also decrease the risk of stroke from a blood clot in adults. But this treatment doesn't appear to decrease the risk of heart disease.

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 is used to look for the two most common MTHFR changes called C677T and A1298C. It's possible to have one or both of these gene changes without having any health problems. An MTHFR gene test may be done alone or as part of a group of genetic tests.

The test may be used to:

• Find out if a common MTHFR gene change is causing increased homocysteine in your blood. But the treatment for high homocysteine is the same whether or not you have a gene change.
• Estimate the risk of developing blood clots or early heart or blood vessel disease. Researchers aren't certain whether homocysteine levels affect the risk of these diseases, so some medical experts recommend against using MTHFR testing for this purpose.

Different types of gene tests are used to look for rare types of MTHFR gene changes that can lead to very high levels of homocysteine in both blood and urine. This causes a serious disease called homocystinuria. Symptoms usually show up in the first year of life. In mild cases, symptoms may not appear until childhood or later. In the U.S., most newborns have a routine screening test to check for signs of homocystinuria.

Why do I need an MTHFR gene test?

In general, medical experts do not recommend testing for common MTHFR gene changes.

But the test may be ordered if:

• You had a blood test that showed higher than normal levels of homocysteine
• 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 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.