Every year in the U.S., doctor’s offices and hospitals order billions of laboratory tests to measure everything from cholesterol levels in the blood to the presence of a gene that is thought to increase the risk of developing Alzheimer’s disease. Physicians and patients typically assume that they can trust the results of these tests, and most of the time they can. But not all lab tests are equally reliable, and faulty ones can have serious consequences. Sometimes they fail to determine life threatening conditions. Other times they indicate a problem that does not exist, which can lead to unnecessary, perhaps even dangerous treatments. The U.S. Food and Drug Administration (FDA) is now taking steps to restore confidence in the reliability of these tests. In 2017, the agency released proposed guidelines that will subject these tests, for the first time, to federal oversight. Several industry sources believe the final rulings may begin taking effect soon, whereas some lab directors say that the requirements could increase costs and affect medical practice.