Recommendations for Provoked Challenge Urine Testing

Anne-Michelle Ruha

"Urine mobilization test," "challenge test," and "provoked urine test" are all terms used to describe the administration of a chelating agent to a person prior to collection of their urine to test for metals. There is no standard, validated challenge test. Despite recommendations by professional and government organizations against the use of provoked urine testing, the tests are still commonly used and recommended by some practitioners. Challenge testing utilizes a variety of chelating agents, including dimercaptosuccinic acid (DMSA), dimercaptopropanesulfonate (DMPS), and ethylenediaminetetraacetic acid (EDTA). The agents are given by a variety of routes of administration, doses used are inconsistent, and urine collection procedures vary. Additional problems with challenge tests include comparison of results to inappropriate reference ranges and creatinine correction of urine obtained within hours of chelator administration. Human volunteer studies demonstrate that mercury is detected in the urine of most people even in the absence of known exposure or chelator administration, and that urinary mercury excretion rises after administration of a chelator, regardless of exposure history and in an unpredictable fashion. Studies also demonstrate that challenge testing fails to reveal a "body burden" of mercury due to remote exposure. Chelating agents have been associated with adverse reactions. Current evidence does not support the use of DMPS, DMSA, or other chelation challenge tests for the diagnosis of metal toxicity. Since there are no established reference ranges for provoked urine samples in healthy subjects, no reliable evidence to support a diagnostic value for the tests, and potential harm, these tests should not be utilized.