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Homocysteine Blood Test

What Is Homocysteine, and Why Measure It?

  • Homocysteine is an amino acid. Amino acids are the building blocks of proteins. When proteins break down, elevated levels of amino acids like homocysteine may be found in the bloodstream.
  • Homocysteine levels increase in the body when the metabolism to cysteine of methionine to cysteine is impaired. This may be due to dietary deficiencies in vitamin B6, vitamin B12, and folic acid.
  • Having elevated levels of homocysteine in the blood (hyperhomocysteinemia) is associated with atherosclerosis and blood clots.
  • You can't get homocysteine from your diet. It has to be made from methionine, another amino acid that is found in meat, fish, and dairy products. Vitamins B6 (pyridoxine), B12 and folic acid are needed to make this reaction occur.
  • Foods containing methionine are transformed into homocysteine in the bloodstream. Homocysteine is converted in the body to cysteine, with vitamin B6 facilitating this reaction. Homocysteine can also be recycled back into methionine using vitamin B12-related enzymes.
  • Cysteine is an important protein in the body that has many roles. It is involved in the way proteins within cells are folded, maintain their shape, and link to each other. Cysteine is a source of sulfide and is part of the metabolism of different metals in the body including iron, zinc and copper. Cysteine also acts as an anti-oxidant.
  • If homocysteine cannot be converted into cysteine or returned to the methionine form, levels of homocysteine in the body increase. Elevated homocysteine levels have been associated with heart attack, stroke, blood clot formation, and perhaps the development of Alzheimer's disease.

What Is Homocystinuria, and How Is It Inherited?

Patient Comments

Homocystinuria (meaning elevated homocysteine in the urine) is a rare, inherited disease in which affected persons have abnormally high levels of homocysteine due to abnormal metabolism of the amino acid methionine. This condition is associated with a number of different birth defects including abnormalities of the musculoskeletal system. In infants who have a family history of homocystinuria, early screening for elevated levels may help prevent future illnesses related to this metabolic defect. Moreover, infants and young children who have eye problems such as myopia (nearsightedness), changes in the lens of the eye, bone abnormalities, or unusual body shape may be screened for elevated homocysteine levels.

What Are the Health Risks for Elevated Homocysteine Levels?

Elevated homocysteine levels in the body do not cause any symptoms. However, elevated levels of it in the blood have been associated with health risks. Therefore, an elevated homocysteine level may be a risk factor for developing certain diseases and conditions. For example:

  • Elevated homocysteine levels affect the interior lining of blood vessels in the body, increasing the risk of atherosclerosis or narrowing of blood vessels. This can result in early heart attack and stroke.
  • There is a relationship between the levels of homocysteine in the body and the size of the carotid arteries that supply the brain with blood; the higher homocysteine level, the narrower (stenosed) the carotid artery becomes.
  • The risk of deep vein thrombosis (DVT) and pulmonary embolism may be linked to elevated homocysteine levels.
  • There may be a relationship between elevated homocysteine levels and broken bones, especially in the elderly.
  • Alzheimer's disease and other types of dementia may be more frequently seen in patients with increased or elevated levels of the amino acid in the blood.
  • In infants who have the genetic condition homocystinuria, the inherited abnormalities affect the body's metabolism of homocysteine to cysteine. This may result in dislocation of the lens in the eye, sunken chest, Marfan-type appearance (long thin body type), mental retardation, and seizures. Neonatal strokes may also be seen with high homocysteine levels.
  • In pregnancy, homocysteine levels tend to decrease. Elevated homocysteine levels may be associated with some fetal abnormalities and with potential blood vessel problems in the placenta, causing abruption. There may also be an association with pre-eclampsia.
Last Reviewed 9/11/2017

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Patient Comments & Reviews

The eMedicineHealth doctors ask about Homocysteine (Blood Test):

Homocysteine - Experience

Please share your experience with high homocysteine levels in the blood. Why you were tested, do you have any risk factors, etc.

Homocysteine - Homocystinuria

If you or your child has homocystinuria, please share your experience in how you manage your condition.

Homocysteine - Lowering Elevated Levels

How have you been able to lower and manage your condition?

Homocysteine - Prevention of Heart Disease

Please share your experience with lowering homocysteine levels and lowering your risk of heart disease and blood clots?

Vitamin B-12 Deficiency and Elevated Homocysteine Levels

Pernicious anemia, or vitamin B-12 deficiency, is a type of anemia that's caused by the body's inability to absorb vitamin B-12 from the gut. Symptoms take many years to appear, and when they do you may experience clumsiness, lack of coordination, and personality changes. One blood test used to diagnose this condition is a homocysteine blood test since elevated levels of homocysteine is characteristic of vitamin B-12 deficiency.

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