What is a methylmalonic acid (MMA) test?

This test measures the amount of methylmalonic acid (MMA) in your blood or urine. MMA is a substance made in small amounts when you digest protein. MMA is needed for metabolism, which is the process that your body uses to change food into energy.

Vitamin B12 plays an important role in metabolism. Part of this role is breaking down MMA into substances that help with metabolism. If your body doesn't have enough vitamin B12, it will continue to make more MMA than is broken down. High MMA levels can be a sign of a vitamin B12 deficiency.

Vitamin B12 deficiency can happen if you are not eating enough B12 in your diet or if your body has difficulty absorbing it. Your body cannot make vitamin B12 on its own, so you have to get it from the foods you eat. This vitamin is found in foods such as:

• Seafood such as fish, clams, and oysters
• Dairy products
• Chicken
• Eggs
• Meat

Vitamin B12 is also found in some fortified foods, meaning the food has vitamins added to it. It's also available as a supplement.

Vitamin B12 also helps to make red blood cells. A deficiency can lead to health issues, including anemia. This is a condition in which your blood has a lower-than-normal amount of red blood cells.

Other names: MMA

What is it used for?

An MMA test is most often used to diagnose a vitamin B12 deficiency.

The test is usually also included as part of a series of tests called a newborn screening. A newborn screening checks for a variety of health conditions. An MMA test checks for methylmalonic acidemia, a rare genetic disorder. Symptoms of this disorder can range from mild to severe and may include:

• Vomiting
• Dehydration
• Developmental delays
• Intellectual disability, which means that a person has trouble with intellectual functioning (such as learning and communicating) and everyday social and life skills.

Why do I need an MMA test?

You may need this test if you have symptoms of a vitamin B12 deficiency. These may include:

• Fatigue
• Diarrhea
• Dizziness
• Shortness of breath
• Loss of appetite
• Tingling in hands and/or feet
• Mood changes
• Confusion
• Irritability
• Pale skin

You might be at a higher risk for B12 deficiency if you:

• Are a strict vegetarian or vegan
• Have a digestive disease, such as celiac disease or Crohn's disease
• Are a person with an alcohol use disorder (AUD)
• Are older than 75 years
• Have Sjogren's syndrome, a disease that causes dry eyes and mouth
• Have had certain types of stomach or intestinal surgery

If you have a new baby, they will probably be tested as part of a newborn screening.

What happens during an MMA test?

MMA levels may be checked in blood or urine.

During a blood 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.

During a newborn screening, a health care provider will clean your baby's heel with alcohol and poke the heel with a small needle. The provider will collect a few drops of blood and put a bandage on the site.

MMA urine testing may be ordered as a 24-hour urine sample test or a random urine test.

For a 24-hour urine sample test, you'll need to collect all your urine during a 24-hour period. This is called a 24-hour urine sample test. You'll be given a special container to collect your urine and instructions on how to collect and store your samples. Your provider will tell you what time to start. The test generally includes the following steps:

• To begin, urinate in the toilet as usual. Do not collect this urine. Write down the time you urinated.
• For the next 24 hours, collect all your urine in the container.
• During the collection period, store the urine container in a refrigerator or cooler with ice.
• 24 hours after starting the test, try to urinate if you can. This is the last urine collection for the test.
• Return the container with your urine to your provider's office or the laboratory as instructed.

For a random urine test, your sample of urine may be collected any time of the day.

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

You may need to fast (not eat or drink) for several hours before your test. Your provider will let you know if there are any special instructions to follow.

Are there any risks to the test?

There is very little risk to you or your baby during an MMA blood test. You may experience slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

Your baby may feel a little pinch when the heel is poked, and a small bruise may form at the site. This should go away quickly.

There is no known risk to having a urine test.

What do the results mean?

If your results show higher-than-normal levels of MMA, it may mean you have a vitamin B12 deficiency. The test can't show how much of a deficiency. To help make a diagnosis, your provider may compare your results with other tests including a homocysteine blood test and/or vitamin B tests.

Lower-than-normal levels of MMA are not common and are not considered a health problem.

If your baby has moderate or high levels of MMA, it may mean that they have methylmalonic acidemia. If it's not treated, it can cause life-threatening complications. If your baby is diagnosed with this disorder, talk to your child's provider about treatment options.

If you have questions about your results, talk to your provider. Your provider will consider your symptoms, medical history, and the results of other blood tests.

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