Homocysteine: what it is, what it tells you and when it’s tested

Homocysteine is an amino acid your body makes every day as it breaks down protein. To clear it, your body needs three vitamins: B12, folate and B6. If one is short, or your kidneys work less well, homocysteine builds up in your blood.

When it’s tested

Doctors mostly order it in three cases: when they suspect a shortage of B12 or folate, after a heart attack, stroke or blood clot at a young age, or when similar cases run in the family.

It is not a routine test for people who feel well. A high homocysteine is linked to a higher risk for your heart and arteries, but in trials, lowering it with vitamins did not reduce heart attacks.

That is why Rosa does not test it. Instead it looks at what most often pushes it up: vitamin B12, MCV, which picks up B12 and folate shortages, and your kidneys.

What it tells you, and what it does not

If it is high, B12 or folate is often short. It is a useful signal: sometimes it rises before the shortage shows on other tests.

It does not say which vitamin is missing, though, or whether your heart risk is high. Other tests and an examination answer that.

If it is normal, your B vitamins are usually enough.

That is why it is read together with other tests:

• Vitamin B12: A shortage is one of the most common causes
• Folate: Even a little too little folate raises it
• MCV: Large red cells point to B12 or folate
• Creatinine: If your kidneys work less well, it rises

Normal homocysteine levels

The lab decides what is normal. Many lab reports give 5 to 15 µmol/L. Your own report may print different limits, sometimes different for men and women.

It tends to be a little higher in men and with age. It falls in pregnancy.

The blood test is done fasting, and the tube must be processed soon: if it sits for a long time, the value rises on its own.

What your result means

Find the row for your result, in µmol/L. Which values need a doctor? Above 15; above 30, soon.

• Below 5: Low. Usually not a problem. It is common in people who take folic acid or B vitamins. Usually nothing to do.
• 5 to 15: Normal. Your body clears it well. B12, folate and B6 are enough. Nothing to do. The lower it sits in this range, the better.
• 15 to 30: High. Often B12 or folate is low. Kidneys, thyroid, smoking, coffee and some medicines count too. Talk to your doctor: they usually check B12, folate and your kidneys.
• Above 30, up to 100: Very high. Usually a marked shortage of B12 or folate, or kidneys that work less well. See your doctor soon. The cause needs to be found and treated.
• Above 100: Extremely high. This is rare. It can be a severe B12 shortage or an inherited metabolic condition. See your doctor within a few days: they usually refer you to a specialist.

If your homocysteine is high or low

• High homocysteine: Usually B12 or folate is short. It is often corrected with diet or the right vitamins.
• Low homocysteine: Not a problem. It is common in people who take B vitamins.

What can skew the result

A few things raise it without any shortage. It helps to know them before your blood test.

• A protein-rich meal: Meat or cheese the evening before can raise it a little. That is why the test is done fasting.
• A tube left standing: If the sample is not processed soon, the value rises. That is a lab error, not yours.
• Some medicines: Metformin, methotrexate, anti-epileptics and some stomach medicines can raise it. Tell your doctor.
• Smoking and lots of coffee: People who smoke or drink a lot of coffee often have slightly higher levels.

When to worry

Talk to your doctor if:

• Your homocysteine is above 15 µmol/L.
• It is above 30: see your doctor soon, the cause needs to be found.
• You have tingling in your hands and feet, tiredness that does not go away or memory problems: they can come from a B12 shortage.
• You have had a blood clot, or heart attacks or strokes at a young age run in your family.
• It is above 100: see your doctor within a few days.

Frequently asked questions

What are normal homocysteine levels? Many lab reports give 5 to 15 µmol/L. The range on your own report is what counts.

Do I need to fast for a homocysteine test? Yes. Usually at least eight hours of fasting is asked. You can drink water.

What does MTHFR have to do with homocysteine? MTHFR is a gene that helps your body use folate. A common variant can raise homocysteine a little, especially when folate is low. The genetic test is usually not needed: the homocysteine value and how much folate you get are what count.

Is high homocysteine bad for your heart? People with high homocysteine have, on average, a higher risk for the heart and arteries. But in trials, lowering it with vitamins did not reduce heart attacks. Cholesterol, blood pressure, smoking and blood sugar matter more.

Does Rosa test homocysteine? No. Rosa measures vitamin B12, MCV and creatinine, which say a lot about what raises it. If your doctor wants homocysteine, they order it separately.

Sources

• Refsum and colleagues, facts and recommendations about total homocysteine determinations: an expert opinion. Clinical Chemistry, 2004. PMID 14709635
• Homocysteine Studies Collaboration, homocysteine and risk of ischemic heart disease and stroke: a meta-analysis. JAMA, 2002. PMID 12387654
• Martí-Carvajal and colleagues, homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database of Systematic Reviews, 2017. PMID 28816346
• Hickey and colleagues, ACMG practice guideline: lack of evidence for MTHFR polymorphism testing. Genetics in Medicine, 2013. PMID 23288205