Homocysteine

Pick Ordered or Not ordered to see the note.

Indicated when

• —Second-line workup of suspected vitamin B12 deficiency when the serum B12 level is borderline or discordant with the clinical picture; homocysteine can help clarify a functional deficiency, though it is less specific than methylmalonic acid [2]

Not indicated when

• —General cardiovascular risk assessment or as a target for treatment: a Cochrane review found homocysteine-lowering with B-vitamin supplementation did not reduce myocardial infarction or death from any cause, so measuring homocysteine to guide cardiovascular prevention does not change evidence-based management [1]
• —Routine addition to a wellness or hormone panel without a specific indication

Why not

The reason homocysteine is often proposed, as a modifiable cardiovascular risk factor, isn't supported by the outcomes evidence: a Cochrane review of 15 randomized trials in over 71,000 people found homocysteine-lowering supplementation did not reduce myocardial infarction or death from any cause, compared with placebo [1]. So even where a result is high, treating it doesn't carry the anticipated cardiovascular benefit. Homocysteine is also non-specific: besides B12, it can be affected by B6 or folate status, kidney function, and other factors, so an isolated elevated result outside a specific clinical question is hard to interpret.

Better first step

For suspected B12 deficiency, start with serum B12; add homocysteine (and methylmalonic acid, where available) as a second-line test if the B12 level is borderline or symptoms don't match a normal-looking B12 [2]. For general cardiovascular risk, homocysteine is not the right test; standard risk factors and a lipid panel are.

Typical ND rationale

An ND may order homocysteine reasoning that an elevated level is a modifiable cardiovascular risk factor that standard panels miss, or as a functional marker of B12, B6, or folate status when levels are borderline.

Ontario coverage & CONO orderability

OHIP status

uninsured

Homocysteine does not appear by name anywhere in the 2026 Schedule of Benefits for Laboratory Services, consistent with docs/research/ontario-coverage.md's listing of homocysteine among tests absent from the community Schedule. Absence from the community Schedule doesn't rule out coverage through another pathway, so this is recorded as unverified. ND-ordered testing is patient-paid regardless (Reg. 552 s.22). Coverage update (reconciliation pass): LifeLabs' Non-OHIP Billable Test List (2025, republished by an Ontario hospital lab) lists this test as patient-paid in community labs. This is secondary evidence, not a ministry statement.

CONO orderable

Yes — CONO list #76

CONO list item 76, blood: 'Homocysteine.' Related but distinct CONO items sometimes ordered alongside it: 112 (S-adenosyl methionine), 111 (S-adenosylhomocysteine), 52 (Cystathionine); these are separate analytes with their own indications, not researched in this session and not covered by this record's verdict.

Linked conditions

• Vitamin B12 deficiency ↗
• MTHFR mutation / methylation problems ↗
• tired ↗

Counselling script

“Homocysteine isn't useful for assessing heart disease risk, because lowering it with B vitamins hasn't been shown to prevent heart attacks or reduce death, even though that's the reason it's often ordered. Where it is useful is as a follow-up test when a B12 level is borderline and doesn't fit your symptoms, so I'd only add it in that kind of situation, not as routine bloodwork.”

Revisit if

• —Borderline B12 result with symptoms suggestive of deficiency
• —New neurological or blood count features of B12 deficiency
• —New interest in MTHFR genotype testing (see the MTHFR condition page)

References

1. [1]Cochrane (2017). Homocysteine-lowering interventions for preventing cardiovascular events. linkHomocysteine-lowering supplementation with B vitamins did not reduce myocardial infarction, all-cause mortality, or serious adverse events across 15 RCTs
2. [2]British Committee for Standards in Haematology (2014). Guidelines for the diagnosis and treatment of cobalamin and folate disorders. linkolder guidelinePlasma homocysteine may be a helpful second-line test for clarifying uncertain B12 status, though less specific than methylmalonic acid
3. [3]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkCommunity lab tests are insured only when ordered under the Schedule by an authorized prescriber
4. [4]Government of Ontario (e-Laws) (2026). Health Insurance Act, R.R.O. 1990, Reg. 552: General, s. 22 (insured laboratory services). linkA lab test is insured only when ordered by a physician, midwife, or NP who has clinically assessed the patient
5. [5]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkTests ordered by anyone other than an authorized provider, including NDs, are not insured services
6. [6]LifeLabs (republished by Norfolk General Hospital laboratory) (2025). LifeLabs Non-OHIP Billable Test List (republished by Norfolk General Hospital laboratory, effective 2025). linkListed as a non-OHIP (patient-paid) test at LifeLabs Ontario, 2025