This test measures the amount of a substance called methylmalonic acid (MMA) in your blood.
MMA is typically made in tiny amounts when you digest protein. Your body makes large amounts of MMA if you have a drop in the amount of vitamin B12. MMA is excreted through your kidneys.
Your body needs B12 to make red blood cells and to help your central nervous system function properly. Low levels of B12 can cause anemia, when your body does not make enough red blood cells.
This test is used to diagnose a mild and early shortage of vitamin B12. A high level of MMA can mean that that you have a low level of B12. Vitamin B12 deficiency is the most common cause of MMA production.
Foods that can increase B12 levels include red meats, shellfish, fish, dairy, and cereals fortified with the vitamin. If you are a strict vegetarian, you may be at higher risk for a B12 deficiency. If you are pregnant and are a vegetarian, you may want to take a B12 supplement. This is especially important if you plan to exclusively breastfeed your baby. Otherwise, your child may also be especially susceptible to a B12 deficiency.
You may have this test if your doctor suspects that you have a vitamin B12 deficiency. You may also have this test if you have symptoms of neuropathy, or loss of movement. This can include numbness and tingling in your hands and feet.
Other symptoms of B12 deficiency include:
Numbness in your hands or feet
Difficulty in thinking clearly
You may also have this test if your doctor suspects that you have methylmalonic acidemia, an uncommon metabolic disorder in which your body can't process certain fats and proteins. The disease is usually diagnosed in infants and can be mild or life-threatening.
Your doctor may also order a homocysteine blood test. If your homocysteine levels are high, your doctor may also order a test to measure your folate (folic acid) concentrations.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Results are given in micromolars per liter (mcmol/L). A normal test result is less than 0.2 mcmol/L. It means that you likely have enough vitamin B12 in your body.
If your MMA levels are higher, you may have a B12 deficiency.
Higher MMA levels are common in pregnancy. Higher MMA levels may also be caused by kidney disease. This is usually because less MMA is sent into your urine, causing it to accumulate in your blood.
Infants may have extremely high levels of MMA because of a condition called methylmalonic acidemia. B12 levels typically return to normal with treatment.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
Other factors aren't likely to affect your results.
You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.