The newly approved molecular expression test, called "AlloMap," "can help contribute to an appropriate treatment plan by identifying those patients not experiencing post-operative heart transplant rejection," said Dr. Daniel Schultz, director of the FDA's Center for Devices and Radiological Health. "It is an example of how advancements in science and technology are leading to new medical care diagnostics."

The FDA said AlloMap measures genetic information contained in a heart transplant patient's white blood cells and then generates a score that indicates whether that patient is likely to reject the new organ.

Clinicians currently rely on a heart biopsy to gauge whether a patient is rejecting the transplanted heart, the federal agency said. However, biopsies are difficult to perform and can be risky for the patient.

According to the National Heart, Lung and Blood Institute, half of all possible rejections occur during the first six weeks after surgery and 25 percent of patients have signs of possible rejection at least once during the first year following a transplant.

The test was developed by XDx Inc. of Brisbane, Calif.