Excess mercury in the tissues is tightly bound to sulphur-containing amino acids and normally poorly excreted into the urine. The oral administration of 15 mg of DMSA per kg body weight is used to provoke the release and excretion of mercury; subjects with excess tissue storage of mercury will at least double their urine concentration of the metal over a 2.5 hour period post oral DMSA. In the absence of excess metal sequestration no significant increase in urinary mercury excretion will be observed. DMSA will also chelate other heavy metals, so while this is primarily used as a challenge test for mercury overload, other toxic metals can also be usefully measured in the urine samples provided.
The patient can eat and drink normally (but not excessively) during this test, which can be carried out at home. The dosage of DMSA used should be calculated from the subject's current body weight.
Mercury is a toxic metal with no known biological essentiality in man and its presence in any concentration can be regarded as harmful under certain circumstances.There is no clearly defined reference interval for the increment in mercury production post DMSA; ideally the molar mercury/creatinine ratio in the basal sample should be less than 0.50, while that in the DMSA-provoked sample should be less than 1.00. The reference interval quoted on the report for the basal urine mercury/creatinine ratio (less than 2.00) reflects the current excessive dietary and environmental intake of mercury in this population.However, a "normal" DMSA provocation test result (i.e. no excessive body mercury present) can be taken as an increase in urine mercury (corrected for creatinine concentration) of less than 100 % (= twice the initial value) and below 2.00 mmol Hg per mole of of creatinine.Co-administration of chelating agents and other substances promoting metal excretion will influence the results of the DMSA provocation test, principally to raise the basal mercury/creatinine ratio and blunt the response to DMSA.
2 x urine samples