Homocysteine Test

What is a homocysteine test?

A homocysteine test measures the amount of homocysteine in a sample of your blood. Homocysteine is an amino acid. Amino acids are molecules that your body uses to make proteins.

Normally, your homocysteine levels are low. That's because your body uses vitamin B12, vitamin B6, and folic acid (also called folate or vitamin B9) to quickly break down homocysteine and change it into other substances that your body needs. High levels of homocysteine in your blood may be a sign that this process isn't working properly or that you're lacking certain B vitamins.

High levels of homocysteine can damage the inside of your arteries and increase your risk of forming blood clots. This may increase your risk for heart attack, stroke, and other heart diseases and blood vessel disorders.

Other names: total homocysteine, plasma total homocysteine

What is it used for?

A homocysteine test may be used to:

• Find out if you're lacking vitamin B6, B12, or folic acid. These vitamins break down homocysteine. So if you don't have enough of them, your homocysteine levels will increase. A homocysteine test may be done with a blood test to measure your vitamin B levels.
• Help diagnose homocystinuria. Homocystinuria is a rare, genetic disease that prevents your body from using a certain amino acid to make important proteins. Symptoms usually show up in the first year of life, but they may not appear until childhood or later. Common symptoms include problems with eyesight, blood clots, and weak bones. In the U.S., most newborns have a routine screening test to check for homocystinuria.
• Better understand your risk for heart attack or stroke if you already have an increased risk. Your health care provider may order a homocysteine test if you have been diagnosed with heart or blood vessel disease or if you have conditions that increase your risk for heart and blood vessel disease, such as:
  • High blood pressure
  • High cholesterol
  • Diabetes

Medical experts don't recommend routine homocysteine testing to screen for heart disease risk in everyone. That's because researchers aren't sure how much homocysteine levels affect heart and blood vessel diseases. And so far, studies have shown that lowering homocysteine levels doesn't reduce the risk of heart attack or stroke.

Why do I need a homocysteine test?

You may need this test if you have symptoms that suggest you lack vitamin B12 or folic acid. The symptoms may be very mild to severe and may include:

• Dizziness
• Fatigue and/or weakness
• Headache
• Heart palpitations (racing or pounding heart)
• Changes in the color of your skin or fingernails
• Sores on your tongue or in your mouth
• Tingling or numbness in your hands, feet, arms, and/or legs

Your provider may order this test if you have a high risk for low levels of vitamin B12 or folic acid because you:

• Have malnutrition.
• Are an older adult. Older people often can't absorb enough vitamin B12 from food.
• Have alcohol use disorder or a drug addiction.

Your provider may recommend this test if you:

• Have had a heart attack or stroke
• Have one or more conditions that increase your risk for heart attack or stroke, such as high LDL "bad" cholesterol or high blood pressure

What happens during a homocysteine 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 may need to fast (not eat or drink) for 8–12 hours before a homocysteine test. Some medicines and supplements may affect your test results. So, tell your provider about all medicines and supplements you take, especially vitamin B. But never stop taking any medicines unless your provider tells you to.

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?

A high homocysteine level may be a sign that:

• You are not getting enough vitamin B12 or folic acid in your diet.
• You (or your child) have homocystinuria. You will probably need more testing to rule out or confirm a diagnosis of homocystinuria.
• You may have a higher risk of heart disease, stroke, or other blood vessel disorders.

Higher than normal homocysteine levels may also happen with other conditions, such as osteoporosis, chronic kidney disease, hypothyroidism, or Alzheimer's disease or other types of dementia.

If your homocysteine levels are high, it doesn't always mean you have a medical condition that needs treatment. Your results may be affected by:

• Your age. Homocysteine levels may get higher as you get older.
• Your sex. Males usually have higher homocysteine levels than females, but levels in females increase after menopause.
• Smoking

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 a homocysteine blood test?

If you have high homocysteine levels, your provider may suggest that you make changes in the foods you eat. Eating a balanced diet can help you get the right amount of vitamins. If you're considering taking vitamin supplements, talk with your provider first. Research has not shown that reducing homocysteine levels can reduce your risk of heart attack or stroke.