Homocysteine Test

A homocysteine test is a blood test. It measures the amount of homocysteine, an amino acid in the body. The test is often used to diagnose vitamin B6, B9 or B12 deficiency. People with elevated homocysteine may have a higher risk for cardiovascular disease. In newborns, homocysteine testing can help diagnose a rare condition called homocystinuria.


What is a homocysteine test?

A homocysteine test is a blood test that measures the amount of an amino acid called homocysteine in your body.

Homocysteine is a chemical that exists in small amounts in your blood. Vitamins B6, B9 and B12 help break down homocysteine, changing it into other substances your body needs. This process should leave behind very small levels of homocysteine in your blood.

But if the process isn’t working properly, your level of homocysteine may be high. Homocysteine can build up in your blood arteries, increasing your risk of cardiovascular disease, specifically:


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When is a homocysteine test performed?

A homocysteine test often helps healthcare providers:

  • Identify a vitamin deficiency (shortage) of B6, B12 or B9, also known as folate or folic acid.
  • Assess heart disease or stroke risk.
  • Monitor people with heart disease to determine whether the condition is worsening.

Homocysteine testing also may be part of newborn screening. It can identify a rare inherited condition called homocystinuria. The disorder means your body can’t process certain amino acids.

What are the symptoms of vitamin B deficiency?

Your healthcare provider may order a homocysteine test if they suspect you aren’t getting enough vitamin B. Symptoms of a vitamin B deficiency may include:


Who performs a homocysteine blood test?

A healthcare provider such as a nurse, doctor, phlebotomist or laboratory technician takes a blood sample for the test. Then, staff in a laboratory measure the level of homocysteine in the blood.

Test Details

How do I prepare for a homocysteine level test?

Your healthcare provider will give you specific instructions for the test. You may have to fast for eight to 12 hours. That means you shouldn’t eat or drink anything besides water.

You should also tell your healthcare provider about any prescription or over-the-counter medications you take, including supplements. They may affect the results of homocysteine testing.


What should I expect during a homocysteine test?

It takes only a few minutes to collect your blood. In an office, clinic or lab, a healthcare provider will:

  • Wrap a band tightly around your upper arm.
  • Clean an area of your skin.
  • Insert a needle into a vein inside the elbow area, which may cause a stinging or pinching feeling.
  • Attach a tube to the needle and fill the tube with blood.
  • Remove the band and needle, then put pressure on the puncture wound to help stop any bleeding.
  • Place a bandage on your skin.

What can I expect after a homocysteine test?

Your healthcare provider may ask you to keep the bandage on for a few hours. You may also need to avoid exercise for a few hours after the blood test.

What are the risks of a homocysteine test?

Blood tests are very safe and involve little risk. You may have a small bruise where the needle went into the skin. Rarely, the vein may swell. Warm compresses can help.

Results and Follow-Up

When should I get homocysteine test results?

Homocysteine test results are usually available in a day or two, depending on the lab.

What do homocysteine results mean?

Normally, your homocysteine should be less than 15.1 µmol/L. What’s considered normal may differ slightly from lab to lab.

Your healthcare provider will talk to you about the results and what they mean for you. High homocysteine might mean that you:

  • Aren’t getting enough vitamins because you’re malnourished, have poor nutrition or can’t absorb enough dietary vitamins.
  • Consume more alcohol than the recommended amount.
  • Have higher risk for heart disease or stroke.
  • Have homocystinuria, which requires additional testing.
  • Have another health condition, such as hypothyroidism or Alzheimer’s disease.

However, higher homocysteine levels don’t necessarily mean you have a medical condition. Your healthcare provider will consider many factors besides homocysteine level to make decisions about your health, such as:

  • Age, as men generally have higher levels.
  • Menopause, because homocysteine increases in postmenopausal women.
  • Medications that can elevate homocysteine.
  • Smoking history, which can affect homocysteine levels.

A note from Cleveland Clinic

A homocysteine test is a simple blood test. A high homocysteine level may indicate a vitamin deficiency, higher risk for cardiovascular disease or another health condition. Your healthcare provider will talk to you about your results, other important factors and what it all means for you.

Medically Reviewed

Last reviewed on 02/02/2022.

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