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Homocysteine Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Homocysteine Test

A homocysteine test measures the levels of this amino acid in your blood to help identify vitamin deficiencies or assess risks for heart and blood vessel disorders.

What is a homocysteine test?

A homocysteine test measures the amount of homocysteine, an amino acid, in your blood. Normally, your body uses vitamin B12, vitamin B6, and folic acid to break down homocysteine. High levels of this amino acid may indicate that this process is not working correctly or that you are deficient in these B vitamins. If homocysteine builds up in your arteries, it can cause damage and increase the risk of blood clots, heart attack, and stroke.

What is it used for?

The test is most often used to check for deficiencies in vitamin B6, B12, and folic acid, which can lead to anemia, nerve damage, or cognitive decline. It may also be used to:

  • Diagnose homocystinuria: A rare genetic condition that prevents the body from breaking down homocysteine.
  • Assess heart disease risk: For patients already diagnosed with heart or blood vessel disease, or those with high blood pressure, high cholesterol, or diabetes.

Routine screening for heart disease risk is not recommended for everyone, as studies show that lowering homocysteine levels does not always reduce the risk of heart attack or stroke.

Why do I need a homocysteine test?

You may need this test if you show symptoms of vitamin B12 or folic acid deficiency, such as dizziness, fatigue, weakness, headache, heart palpitations, skin or fingernail color changes, mouth sores, or tingling/numbness in your limbs. You may be at higher risk for these deficiencies if you have malnutrition, are an older adult, or have alcohol or drug use disorders.

What happens during a homocysteine test?

A health care professional will draw a small amount of blood from a vein in your arm. The procedure is quick, usually taking less than five minutes.

Will I need to do anything to prepare?

You may be required to fast for 8–12 hours before the test. Inform your provider about all medications and supplements you take, especially vitamin B, as these can affect results. Do not stop taking any prescribed medication unless instructed by your provider.

What do the results mean?

High homocysteine levels may indicate a vitamin B12 or folic acid deficiency, homocystinuria, or an increased risk of heart disease and stroke. Elevated levels are also associated with conditions like osteoporosis, chronic kidney disease, hypothyroidism, schizophrenia, and dementia. Note that results can be influenced by age, sex, and smoking status.

Frequently Asked Questions

Elevated homocysteine can damage blood vessel walls and promote clot formation, which may worsen hypertension and increase cardiovascular risk. Checking the level helps identify a modifiable risk factor that can be addressed with diet or supplements.
High homocysteine is linked to endothelial dysfunction, atherosclerosis, and hypercoagulability—all of which can raise the likelihood of ischemic stroke. Lowering homocysteine may help reduce this risk, especially in patients with existing vascular disease.
Increase intake of leafy greens, legumes, whole grains, and fish, which provide folate, B12, and B6. Reduce consumption of processed meats and limit alcohol, as these can raise homocysteine. Regularly monitoring levels can guide whether dietary changes alone are sufficient.
Supplementation with folic acid, vitamin B12, and vitamin B6 can lower homocysteine in many people, particularly those with deficiencies. However, large trials have shown mixed results on heart‑attack prevention; the benefit may be greatest in individuals with very high baseline levels or confirmed deficiencies. Discuss with your clinician whether supplementation is appropriate for you.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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