WASHINGTON - Government regulators on Wednesday cleared the way for broader use of a blood test that can spare heart transplant patients the ordeal of repeated biopsies to check if their bodies are rejecting the new organ.

The Food and Drug Administration said the test, called AlloMap, is an example of how the science of genetics is changing the practice of medicine.

The test analyzes certain kinds of genetic information contained in white blood cells. These are the cells that help the body fight off infections — but can also turn against a donated organ with devastating effects. After a patient's blood sample is checked in the lab, it is assigned a score that tells doctors what the odds are that the body is rejecting a transplanted heart.

"It is noninvasive," said Dr. James Yee, chief medical officer of XDx, Inc., the California company that devised the test. "It requires only a simple blood sample." The test is especially useful in detecting a "silent rejection"_ one in which there are no evident symptoms, he added. The test costs $2,950.

Heart transplant patients are closely followed for signs of organ rejection, and must visit their doctors frequently. Before the test, doctors relied on a biopsy to check for signs of rejection. A minuscule probe threaded through a vein would be used to snip off a tiny amount of heart tissue, which would then be analyzed by a pathologist. The estimated cost of a such a biopsy ranges from $3,000 to $4,000.

The AlloMap test had been previously approved in 2005 under federal laws that govern clinical labs. But Yee said it is being used at fewer than half of the nation's heart transplant centers, and that FDA clearance should speed its adoption elsewhere.

More than 2,000 heart transplants were performed in the United States in 2006.