In the short term studies, tests that give positive results are repeated to confirm the response. The 13-week micronucleus tests are not repeated, since they are included as part of the NTP subchronic toxicity tests which are not repeated. The micronucleus test provides information that is complementary to the gene mutation information that is obtained from a Salmonella assay. However, there does not seem to be an increased ability to define the carcinogenicity of a chemical by conducting a micronucleus test in addition to a Salmonella assay. Despite the lack of increased predictive value for carcinogenicity, the micronucleus test provides valuable information about the chemical's ability to disrupt mammalian chromosome structure and function.
Most human carcinogens are positive in mammalian micronucleus tests.