Homocysteine
An amino acid that depends on B-vitamin status (B12, folate, B6). High levels are linked to cardiovascular risk and can signal a vitamin shortfall.
Typical reference range
| Range | Unit |
|---|---|
| 5–15 | umol/l |
What Homocysteine measures
Homocysteine is an amino acid your body produces naturally as it breaks down and rebuilds other amino acids during everyday metabolism. Normally it does not build up, because your body converts it back into useful compounds with help from several B-vitamins — chiefly B12, folate, and B6. When those vitamins are plentiful, homocysteine is cleared efficiently and stays low.
This marker is sometimes measured for two reasons: as a possible clue to your B-vitamin status, and as a signal that has been studied in relation to cardiovascular health. Because the two are linked, homocysteine is usually interpreted alongside B12 and folate rather than on its own, and any single reading is best understood in the context of your wider health picture and a clinician's review.
What a high Homocysteine can mean
A higher-than-expected homocysteine most commonly points to low levels of B12, folate, or B6, since these vitamins are needed to clear it. Correcting such a shortfall is the usual reason it comes back toward the expected range.
Other things can raise it too, including reduced kidney function, an underactive thyroid (hypothyroidism), certain medications, and genetic factors such as MTHFR variants that affect folate processing.
Elevated homocysteine has been associated with higher cardiovascular risk in observational studies. It is worth being honest here: trials that lowered homocysteine with vitamins have not clearly reduced heart attacks or strokes, so it is best treated as one clue among many rather than a direct cause. What a raised value means for you, and whether anything (usually correcting a vitamin deficiency) is worth doing, is a conversation to have with a clinician.
What a low Homocysteine can mean
A low homocysteine is generally not a cause for concern and usually needs no action. It often simply reflects good B-vitamin status — ample B12, folate, and B6 keeping the amino acid efficiently cleared, which is what you would hope to see.
It helps to know that the clinical interest in this marker is almost always in high values, not low ones. Low readings are rarely flagged as a problem on their own, and there is no established benefit to trying to push homocysteine even lower.
As with any single number, context matters: the fuller picture comes from how this fits with your other results, your history, and how you feel. If a result raises questions, a clinician can help you read it in that context and decide whether anything further is worth looking into.
Track your Homocysteine over time in Quanome — it reads your lab reports (PDF or photo) on your device, charts each marker against its range, and an AI coach explains what your trends mean alongside your Apple Health and DNA.