Homocysteine, Quantitative
Homocysteine is an amino acid that, when elevated, increases the risk of cardiovascular disease, blood clots, and stroke. High levels may reflect deficiencies in B12, folate, or B6.
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What the Homocysteine, Quantitative test tells you
Homocysteine is an amino acid produced continuously as the body processes methionine, a building block of protein obtained from food. It is not meant to accumulate, because two pathways normally convert it onwards almost as fast as it forms: one recycles it back to methionine and the other diverts it towards cysteine for disposal. Vitamin B12 and folate drive the first pathway and vitamin B6 the second, which is why homocysteine rises when any of the three runs short.
Raised levels have been consistently associated with heart attack, stroke, deep vein thrombosis and disease of the leg arteries, and homocysteine appears to irritate the inner lining of blood vessels and encourage clotting. It is important to be clear about what that does and does not establish. Trials that lowered homocysteine with B vitamins have not shown a corresponding reduction in cardiovascular events, so a raised level is a recognised association rather than a proven treatment target. It is a signal to look for a cause, not a number to be driven down for its own sake.
There are several reasons a level can be high, and separating them is the useful part. Nutritional shortage of B12, folate or B6 is the commonest and the most correctable. Reduced kidney function raises it because the kidneys clear a substantial share. Inherited variation in the enzymes of the pathway, of which MTHFR is the familiar example, makes some people run higher, particularly when folate intake is marginal. Rarely, a severe inherited disorder of methionine metabolism raises it markedly and presents in childhood with a distinctive clinical picture. Your doctor interprets the result against these possibilities together with kidney function and vitamin levels.
Ordered to assess cardiovascular risk, investigate unexplained blood clots, and evaluate B12/folate/B6 nutritional status.
- Reflects B-vitamin status
Homocysteine rises when vitamin B12, folate or vitamin B6 is short, sometimes before other tests of those vitamins change.
- Clarifies borderline B12
When a vitamin B12 result is equivocal, a raised homocysteine supports a genuine functional deficiency rather than a laboratory artefact.
- Investigates unexplained clots
It is checked when a clot has occurred without an obvious cause or at an unusually young age.
- Adds context to vascular risk
A raised level is one additional piece of information in a wider risk assessment, though it is not itself a treatment target.
Reasons your doctor may request the Homocysteine, Quantitative test
Your doctor may order this test for any of the reasons below. Some are routine checks, others follow specific symptoms or an earlier result.
B12 & folate status
- A vitamin B12 result is borderline and your doctor wants to know whether the vitamin is functioning properly.
- A folate or vitamin B12 deficiency is being confirmed or followed up.
Unexplained clots & inherited disorders
- A blood clot has occurred without a clear cause, or at an unusually young age.
- An inherited disorder of methionine metabolism is suspected in a child or young adult.
Cardiovascular risk assessment
- There is a strong family history of early heart disease or stroke.
- Cardiovascular risk is being assessed and standard tests have left questions unanswered.
An "Optimal" µmol/L result means the vitamin-dependent pathways that clear homocysteine are working well. A "Normal" µmol/L result sits within the usual range. A "High" µmol/L result most often points to a correctable nutritional cause (deficiency of vitamin B12, folate or vitamin B6) or to reduced kidney function, since the kidneys clear much of it. Inherited variation in the methionine pathway, including MTHFR variants, an underactive thyroid, methotrexate, some anticonvulsants, metformin and smoking also raise it. A sample left standing before separation reads artificially high. A raised level is associated with vascular disease, but lowering it with B vitamins has not been shown to reduce cardiovascular events, so it is not a treatment target. A low result has no recognised clinical significance. Your doctor interprets it with your vitamin levels, kidney function and symptoms.
Medically reviewed by Dr Nirupama Sabhapathy
Ranges are a guide: your physician interprets your result alongside your symptoms and history.
What a higher result can point to
- Deficiency of vitamin B12, folate or vitamin B6.
- Reduced kidney function, since the kidneys clear a large share of homocysteine.
- Inherited variation in the enzymes of the methionine pathway, including MTHFR variants.
- An underactive thyroid.
- Medicines including methotrexate, some anticonvulsants and long-term metformin.
- Smoking, heavy coffee intake and heavy alcohol use, which raise levels modestly.
These are possibilities, not diagnoses. A single value outside the reference range is interpreted alongside your symptoms, history and other tests: your doctor decides what it means for you.
What this test cannot tell you
- A raised level is associated with cardiovascular disease but is not established as a treatment target, because trials lowering homocysteine with B vitamins have not shown a matching reduction in cardiovascular events.
- Kidney function must be known before the result can be interpreted, since impaired clearance raises it independently of any vitamin problem.
- The specimen is sensitive to handling and must be separated and processed promptly, as a sample left standing gives an artificially raised result.
- A low homocysteine has no recognised clinical significance and is not treated as a finding.
Risks of the blood draw
- Mild bruising or brief soreness where the needle went in.
- Occasional lightheadedness, which settles after a few minutes of rest.
- Bleeding or infection at the site, which is rare with sterile single-use equipment.
- 1Homocysteine accumulates when the vitamin-dependent pathways that clear it are not working well.
- 2Vitamin B12, folate and vitamin B6 are all required, so a raised level often points to a correctable nutritional cause.
- 3Reduced kidney function and inherited enzyme variants are the other common explanations, and a rare inherited disorder raises it markedly.
- 4Raised levels are associated with vascular disease, but lowering them with vitamins has not been shown to prevent cardiovascular events.
- 5It is interpreted alongside vitamin levels and kidney function, never on its own.
Homocysteine, Quantitative is also part of these health checkups, which add a wider screen in the same appointment.
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Frequently Asked Questions
Everything you need to know about the Homocysteine, Quantitative test. Can't find what you're looking for?
Talk to our team→Our laboratory reports 0 to 10 µmol/L as optimal and 10.1 to 15 µmol/L as within the normal range. Above 15 µmol/L is reported as high and may relate to B-vitamin status or cardiovascular risk. A low level has no recognised clinical significance.
The commonest causes are a shortage of vitamin B12, folate or vitamin B6, and reduced kidney function. Inherited variation in the methionine pathway, including MTHFR variants, an underactive thyroid, and medicines such as methotrexate, some anticonvulsants and long-term metformin also raise it, while smoking, heavy coffee and heavy alcohol use raise it modestly.
A raised homocysteine is associated with blood clots, stroke and vascular disease, so it is one of the checks when a clot has no obvious cause. A high result usually leads your doctor to look for a vitamin deficiency, kidney problem or inherited enzyme variation, alongside the other clotting investigations.
The kidneys clear a large share of homocysteine, so reduced kidney function raises it whether or not your vitamins are adequate. Your doctor needs to know your kidney function before reading the result, otherwise a kidney-related rise could be mistaken for a vitamin deficiency.
Yes. Long-term metformin, methotrexate and some anticonvulsants can all raise homocysteine, largely by interfering with the B vitamins and folate that clear it. Mention these when you book, and your doctor may check vitamin B12 and folate alongside. Do not stop any prescribed medicine because of the result.
Homocysteine is made from methionine, an amino acid found in dietary protein, so eating shortly before the sample raises the level directly. Fasting removes that influence and makes results comparable between visits.
Not necessarily. Many people carrying these variants have entirely ordinary levels, particularly when folate intake is good. The variant shifts the odds rather than determining the result.
Vitamins usually lower the number when deficiency is the cause. Whether that lowering translates into fewer heart attacks or strokes has not been demonstrated in trials, so your doctor treats the underlying cause and manages vascular risk in the established ways.
No. It is one narrow piece of information. Blood pressure, lipids, glucose, smoking and family history all carry considerably more weight in an overall cardiovascular risk assessment.
Yes. Take nothing but plain water overnight before the sample, ideally with a morning appointment. If you take vitamin B12, folate or vitamin B6 supplements, ask your doctor whether to pause them beforehand, since they lower the result and can conceal a deficiency.
The homocysteine test is AED 150, including a physician-reviewed report, with results usually within 24 hours. Home collection anywhere in Dubai is free when your order reaches AED 300 or includes a package; below that, a AED 100 home collection fee applies (AED 50 for a lab walk-in).