This test may be vetted by a pathologist.
The clinical information for the test must be clearly written on the request form. If clinical information is not provided, or does not provide sufficient justification for the test, the test may be declined.
Declined tests :
If a test is declined, the specimen will be held for a reasonable period (usually 3 weeks but dependant on the stability of the sample). Medical practitioners seeking approval for a declined test should email the on-call Chemical Pathologist ( chemicalpathologist@adhb.govt.nz ) , giving the patient's name and NHI number and the clinical justification for the test. If unable to email, call the on-call Chemical Pathologist via Lablink (09-3078995) and identify yourself as a doctor.
Whole blood required - DO NOT SPIN
Units: nmol/L
Normal: 0 - 50
Blood mercury levels <50 nmol/L are seen in people who do not have a high fish intake.
Levels up to 100 nmol/L are not uncommon in people who eat fish frequently, especially large predatory types of fish e.g. shark and swordfish.
Toxic effects (neurological damage) are possible with blood mercury levels greater than 250 nmol/L, but the blood mercury level and symptoms do not correlate well, especially in the range between 100-500 nmol/L. A spectrum of increasing risk probably applies in this range.
Uncertainty of Measurement: 20%
Conversion :
ppb x 5 = nmol/L
ug/L x 5 = nmol/L
Principle : Inductively coupled plasma mass spectrometry (ICP-MS)
Instrument : PlasmaQuant MS Elite
Mercury exists in elemental, inorganic and organic forms, all of which may be toxic. The toxic manifestation depends on the form of exposure.
For elemental and inorganic forms, the preferred test depends on whether the patient is suspected of having acute or chronic mercury exposure.
Whole blood should be measured in very recently exposed patients with suspected acute toxicity - whole blood can reflect very large acute exposure but is less reliable as redistribution to tissues takes place
24 hour urine should be measured in patients with suspected chronic (medium to long term) exposure
The preferred test for determining toxicity from organic mercury is whole blood . Because organic mercury is eliminated via the faecal route, urine mercury testing is less useful.
Blood and urine mercury tests measure the total mercury level (both forms).
Determination of mercury in blood is usually done for suspected environmental/occupational exposure. Blood levels indicate recent exposure only and do not relate well to total body burden of mercury in chronic exposure. All forms of mercury (predominantly organic and inorganic) are measured. We do not attempt to separate the components organic and inorganic mercury.
Organic mercury is usually the major fraction of blood mercury. Fish intake is the strongest determinant of blood mercury levels in people not occupationally exposed to mercury.
Mercury levels are highest in large predatory fish at the top of the food chain (e.g. tuna, swordfish, shark).
Dental amalgam makes a minor contribution to body mercury levels. Claims that amalgam fillings cause mercury toxicity are not supported by good evidence.
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.
In women of childbearing age
It is desirable that women of child bearing age have low blood mercury level. Although a "safe" level during pregnancy is not well established some health authorities suggest <40 nmol/L. The toxic effects of high antenatal mercury exposure to newborns has been well described e.g. from Japan. However, at low level especially between 40 and 100 nmol/L, there is no clear relationship with toxicity.
Fish is the main source of mercury in most people. It is advisable to avoid or have limited intake of fish species known to have high mercury content when planning for, or during, pregnancy. On the other hand, that should be balanced against the health benefits that fish species with low mercury content can bring as part of diet. Information on recommended servings for specific fish species can be found at https://www.mpi.govt.nz/food-safety/food-safety-for-consumers/food-and-pregnancy/list-of-safe-food-in-pregnancy/ .
References
1. Mercury: Your Health and the Environment: A Resource Tool. Health Canada Mercury Issues Task Group, 2004 ( http://www.hc-sc.gc.ca )
2. Clarkson TW, Magos L. The toxicology of mercury and its chemical compounds. Crit Rev Toxicol. 2006;36:609-662
3. McKelvey W, Gwynn RC, Jeffery N et al. A biomonitoring study of lead, cadmium, and mercury in the blood of New York city adults. Environ Health Perspect. 2007;115:1435-1441
4. Mercury Toxicity - http://www.uptodate.com/contents/mercury-toxicicty
5. Legrand M, Feeley M, Tikhonov C et al. Methylmercury blood guidance values for Canada. Can J Public Health. 2010;101:28-31
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427
Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427