Mercury testing is usually done when there is excessive exposure to mercury. The mercury levels can be tested by mainly a blood test and or urine test. The doctor would suggest this test if the patient is showing symptoms of mercury poisoning or to measure the occupational exposure of Mercury. Blood test is done to detect the presence of Methyl Mercury or the other compounds of mercury formed by the interaction of mercury with carbon based compounds. Slight exposure to mercury is not dangerous. The mercury gets collected in the organs like kidneys, brain and liver. Kidneys filter out the mercury, but if the exposure is to a large quantity of mercury, then kidneys are not capable to remove the excess mercury and thus it causes organ failure.