Mercury (Urine)

Diagnostic Use

Mercury exists in elemental, inorganic and organic forms, all of which may be toxic. The toxic manifestation depends on the form of exposure.

Whole blood testing should be performed:

1. In very recently exposed patients with suspected acute toxicity. This method is less accurate after redistribution of mercury through the tissues.
2. Patients exposed to organic forms of mercury, since this is eliminated primarily by the faecal route (and less so in the urine).

24 hour urine testing should be measured in patients with suspected chronic (medium to long term) exposure to elemental or inorganic forms of mercury.

Toxic effects of mercury:  Irreversible neurological damage (central and peripheral nervous system) is the most important, but other organs are also affected e.g. renal tubular damage. Toxic effects have been clearly demonstrated at blood mercury levels >1000 nmol/L,  and levels >500 nmol/L should be regarded as indicating high risk.

The clinical effects of levels between 100 and 500 nmol/L are uncertain. Obvious toxicity in adults has not been reported at these levels. However the foetal brain is more sensitive to mercury, and subtle effects on cognitive and fine motor performance in children have shown correlations with cord blood mercury levels in this range in some studies.

Non-specific symptoms such as memory loss, cognitive decline, or chronic fatigue syndrome are not a sufficient indication for measuring blood or urine mercury. There is no evidence that mercury has any causal relationship to autism spectrum disorder.

The half-life in blood is 42 days for inorganic mercury and 45-70 days for organic mercury.

Interpretation

There is poor correlation between the urine mercury level and the clinical symptoms, but urine mercury is the most reliable biomarker to assess chronic exposure to inorganic mercury.

For an assessment of occupational exposure, a casual urine sample should be taken prior to the work shift. The Biological Exposure Index (BEI) by WorkSafeNZ for urine mercury is 11 nmol/mmol creatinine (20 ug/g creatinine). Workers using mercury compounds should be removed from exposure if the urinary level is greater than 11 nmol/mmol creatinine (20 ug/g creatinine).

Urine levels from mercury amalgam dental fillings are generally well below the 50 nmol/d threshold.

Chelation therapy following exposure can be monitored by mercury urine output. The reference intervals given above are not applicable if a chelating agent has been administered.

“Provoked” testing of urine mercury and other metals following chelator administration (e.g. DMSA) is not a valid way to assess metal toxicity.

Reference Intervals

Reference Intervals* [1, 2] [3]

*Reference intervals were updated on 24/9/19 following a literature review and in-house data evaluation.

Occupational exposure: Biological Exposure Index (BEI) by WorksafeNZ 2018 [4] for urine mercury is 11 nmol/mmol creatinine (20 ug/g creatinine). Samples should be taken prior to the work shift.

For the latest Worksafe document click on the link below

The reference intervals DO NOT APPLY if a chelating agent such as DMSA has been administered before collecting the urine.

Conversion :1 ug = 5 nmol1 nmol = 0.2 ug

ug/g creatinine x 0.565 = nmol/mmol creatinine

Worksafe exposure standards and biological indices