Rejection hurts, but organ transplant rejection hurts worse, and XDx wants to help. The company makes tests that monitor for cellular rejection in heart transplants. Its FDA-approved AlloMap test measures gene expression in patients' blood samples to determine if a transplanted heart has been accepted. The company believes its tests will help reduce costs by decreasing the number of biopsies and drug therapies often used in evaluating transplants in patients. XDx also has explored the development of AlloMap for lung transplant patients, and it has other molecular (gene-based) diagnostic research programs in areas such as immunology.