Summary

• Homocysteine is an amino acid that is broken down in the body by vitamins B12, folate (B9) and B6.
• Normally, homocysteine levels are low and high levels in the blood are a sign that this process may not be working properly or that you are lacking B vitamins.
• A homocysteine test is most often used to diagnose deficiencies in vitamin B12 and folate, and less commonly vitamin B6.
• It is also used to screen babies and infants for a rare metabolic disorder called homocystinuria.

What is homocysteine?

Homocysteine is an amino acid. Amino acids are molecules that make up proteins, the building blocks our bodies use to grow and function. Vitamins B12, folate (B9) and B6 help break down homocysteine, changing it into other substances your body needs, such as antioxidants.

Normally, homocysteine levels are low. High levels of homocysteine in your blood may be a sign that this process is not working properly or that you are lacking B vitamins.

Why get tested?

Low vitamin B12, folate (B9) and vitamin B6

A homocysteine test is most often used to assess vitamin B12, folate (B9) and B6 levels. Vitamin B6 deficiency is a less common cause of elevated homocysteine and is usually considered only when B12 and folate levels are normal. A lack of B vitamins (a deficiency) can lead to health problems such as certain types of anaemia and neurological disorders (conditions that affect your nervous system).

These deficiencies occur when your body is either not getting enough of these vitamins through your diet or not absorbing enough because of a malabsorption disorder in your intestines.

If your doctor suspects that you have a deficiency in vitamin B12 and folate they will order a Total B12 as the first-line test. If total B12 results are unclear or borderline the lab will perform a homocysteine test as a reflex test on the same blood sample. A reflex test is an additional test that is triggered automatically based on predefined rules. Another test, active B12 can be measured but only in specific clinical situations. For more on this see Vitamin B12.

Homocystinuria (HCU)

Homocysteine testing of babies and infants is used to help screen for a metabolic disorder called homocystinuria (HCU). This is a rare inherited genetic condition in which the body cannot process homocysteine properly. Homocysteine builds up and damages the eyes, brain, bones and blood vessels, increasing the risk of dangerous blood clots.

Although there is no cure for HCU, it is a treatable condition. In Australia, babies are screened for HCU via the newborn heel prick test. This test measures methionine levels, rather than directly measuring homocysteine.

Methionine is another amino acid taken in from food we eat. It is used by the body to make a substance called s-adenosylmethionine that acts like a switch turning on many processes in the body. After doing its job, methionine is changed into homocysteine.

Cardiovascular (CVD) risk

Homocysteine levels can be measured to better understand cardiovascular risk, particularly in people who already have risk factors such as high blood pressure, high cholesterol or diabetes, or in those with a strong family history of coronary artery disease. However, homocysteine testing is not routinely recommended for cardiovascular risk assessment because lowering homocysteine with folic acid or B‑vitamin supplements has not been shown to reduce the risk of heart attack or stroke.

Having the test

Sample

Blood.

Any preparation?

There are many medications that can either increase or decrease the amount of homocysteine in your body. Also, some recreational drugs can affect levels. You should discuss this with your doctor as they may interfere with the test results.

Your results

Reading your test report
Your results will be presented along with those of your other tests on the same form. You will see separate columns or lines for each of these tests.

High homocysteine levels are seen with vitamin B deficiencies.

Higher homocysteine levels are an early warning sign of vitamin B deficiencies. This is because homocysteine can begin to build up in your blood and your homocysteine levels rise before a clear deficiency shows up in vitamin B blood tests.

For this reason, some healthcare practitioners order homocysteine testing in people at risk of deficiency, such as those who are malnourished, the elderly (who may have reduced absorption of vitamin B12) or people with poor nutrition, including those with drug or alcohol dependence.

Not all elevated homocysteine is due to vitamin deficiency. Other causes include kidney disease, certain medications and lifestyle factors such as smoking.

In newborn testing, greatly increased homocysteine in the blood means that it is likely that an infant has homocystinuria and indicates the need for further testing to confirm the cause of the increase.

Treatment for high homocysteine levels usually focuses on vitamin supplementation and changes to diet. Green leafy vegetables and fortified cereal grains are major sources of folate (vitamin B9). Fruits and vegetables have significant amounts of vitamin B6, and vitamin B12 can be found in red meats, poultry, fish and other seafood.

Reference intervals - comparing your results to the healthy population

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• They are used to provide a benchmark for interpreting a patient's test results.
• When compared against them, your results may be flagged high or low if they sit outside this range.
• Some reference intervals are harmonised or standardised, which means all labs in Australia use them.
• Others are not because for these tests, labs are using different instruments and chemical processes to analyse samples.
• Always compare your lab results to the reference interval provided on the same report.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation.

Reference intervals for homocysteine vary between laboratories in Australia because they use different measurement instruments. Always check your specific laboratory’s ranges.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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