It is possible to test samples of blood, urine, and hair to determine how much mercury people may have in their systems. Blood tests are most useful if there has been recent exposure to mercury. Tests of blood and hair can show exposure to methylmercury. Urine tests are most useful to test for exposure to mercury vapor. If the tests indicate high levels of mercury, X-rays and additional blood and urine tests may show the extent of damage to the lungs and kidneys. Breast milk can also be tested.