LOS ANGELES — A genetic test that looks for activation of genes involved in the rejection of transplanted hearts may be as good as the conventional technique of heart biopsies, but is much less invasive, Stanford researchers reported online Thursday in the New England Journal of Medicine.

The findings are “an important advance in the assessment of noninvasive methods for monitoring rejection after heart transplantation,” wrote Dr. John Jarcho, a deputy editor of the journal, in an editorial accompanying the report. But the findings also suggest that routine monitoring for rejection may not be necessary after the crucial first year.

About 2,200 heart transplants are performed each year in the United States, a number that is limited primarily by the low availability of donor organs. About one-quarter of the recipients will have a rejection episode requiring medical treatment in the first 12 months after the surgery, and acute rejection is responsible for 12 percent of deaths in the first year.

Heart specialists check for rejection by biopsies, inserting a thin catheter through a vein in the neck, threading it to the heart and snipping off a small piece of tissue that can be examined under a microscope. Such tests are often performed weekly in the immediate aftermath of the transplant, then less frequently over time. The risk of a serious complication arising from the biopsy itself is about 1 percent, but the procedure terrifies patients, said Dr. Hannah Valentine of Stanford, the lead author of the new report.

The new test, called AlloMap and developed by XDx Inc. of Brisbane, Calif., measures the activity of 11 genes and those levels are used to calculate a score that measures the likelihood that a rejection episode is occurring.