Mercury (blood and urine)

Pick Ordered or Not ordered to see the note.

Indicated when

• —Suspected organic mercury (methylmercury) exposure, most often from frequent consumption of high-mercury fish (fresh/frozen tuna, shark, swordfish, marlin, orange roughy, escolar): measured with a blood mercury level [1]
• —Suspected inorganic or elemental mercury exposure (occupational/industrial sources, or certain skin-lightening cosmetic products): measured with a urine mercury level [1]
• —Dietary history suggesting risk, pregnancy or planning pregnancy, or occupational exposure to organomercury compounds [2]

Not indicated when

• —Routine or 'wellness' screening for fatigue or nonspecific symptoms with no exposure history suggesting risk [2]
• —Based on the presence of dental amalgam fillings alone: exposure from amalgams is generally negligible, their presence is not an indication for testing, and removing them to reduce mercury exposure is not recommended [1]
• —Collected within 21 days of a chelating agent as a 'provoked' or challenge test (see Provoked (post-chelation-challenge) urine heavy metals testing) [1]

Why not

Reported laboratory reference ranges represent population averages, not toxicity thresholds, and the wrong specimen for the exposure in question can mislead: blood mercury reflects organic (methylmercury, mainly dietary) exposure, while urine mercury reflects inorganic/elemental exposure, so ordering blood mercury to investigate a suspected occupational elemental-mercury exposure (for example) would likely miss it [1]. Testing without an exposure history mostly returns a background-level result that doesn't change management and can generate unnecessary worry.

Better first step

Take an exposure history first: diet (frequency of high-mercury fish), occupation, use of skin-lightening or other mercury-containing cosmetic products, and reassurance that dental amalgams are not an indication for testing. Order blood mercury for suspected organic/dietary exposure and urine mercury for suspected inorganic/elemental exposure, collected without a preceding chelating agent.

Typical ND rationale

An ND may order mercury testing to investigate a 'toxic burden' behind fatigue, cognitive complaints, or other nonspecific symptoms, sometimes anchored to dental amalgams or general fish consumption rather than a specific, quantified exposure.

Ontario coverage & CONO orderability

OHIP status

insured

L168 Mercury is listed in the 2026 Schedule of Benefits for Laboratory Services with no restricting condition, so it is insured when a physician orders it after clinically assessing the patient [5, 7]. The Schedule line does not distinguish a blood versus urine specimen; this record could not verify whether both specimen types bill identically under L168, and marks that detail unverified. ND-ordered testing, blood or urine, is patient-paid regardless [8]. Public Health Ontario's own laboratory stopped performing trace-metal testing, including lead, in 2019 and redirects submitters to other Ontario providers; whether that discontinuation also covered mercury specifically was not confirmed this session ([9] describes lead, aluminum and zinc protoporphyrin by name, not mercury).

CONO orderable

Yes — CONO list #93

CONO list item 93, blood: 'Mercury.' The CONO list has no separate single-analyte urine mercury item; NDs order urine mercury as part of CONO item 166, 'Toxic Metals' (urine panel) — see the Provoked (post-chelation-challenge) urine heavy metals testing record for that item's scope and the provoked-protocol caveat.

Linked conditions

• Heavy metal toxicity (lead, mercury, arsenic, and others) ↗
• tired ↗

Counselling script

“If your diet, job, or a product you use puts you at real risk of mercury exposure, this test is worth doing, and I'll pick blood or urine depending on the type of exposure. Amalgam fillings alone aren't a reason to test, and removing them isn't recommended for lowering mercury. Without an exposure like that, I wouldn't add it to routine bloodwork.”

Revisit if

• —A new occupational exposure or high-mercury fish intake pattern develops
• —Symptoms of mercury toxicity appear (paresthesias, tremor, ataxia, erethism, gingivostomatitis)
• —Pregnancy or planning pregnancy with a risk factor for mercury exposure

References

1. [1]Public Health Ontario (2026). Clinical Evaluation for Mercury Exposure: A Simplified Approach (1st revision). linkOrganic mercury measured by blood level, inorganic/elemental by urine level; amalgams are not an indication for testing and removal is not recommended; provoked testing is not validated; population reference and guidance values
2. [2]Occupational Medicine Specialists of Canada (Choosing Wisely Canada) (2022). Choosing Wisely Canada: Using Labs Wisely – Full List of Recommendations. linkDon't order blood mercury levels unless dietary history suggests risk, pregnancy/planning pregnancy, or occupational organomercury exposure
3. [3]Health Canada (2019). Mercury in Fish Consumption Advice: Making Informed Choices about Fish. linkMost Canadians don't need to be concerned about mercury exposure from fish; specific high-mercury species have consumption limits
4. [4]American College of Medical Toxicology (2009). ACMT Position Statement: Post-Chelator Challenge Urinary Metal Testing. linkolder guidelinePost-challenge (provoked) urine metal testing, including for mercury, is not scientifically validated
5. [5]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026) - L168 Mercury. linkL168 Mercury is listed in the 2026 OHIP Schedule with no restricting condition
6. [6]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
7. [7]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
8. [8]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
9. [9]Public Health Ontario (2019). Lead – Blood and Urine Testing (Test Information Index). linkPublic Health Ontario Laboratory discontinued trace metal testing in 2019, redirecting to other Ontario providers