U.S. researchers said Wednesday they have developed a simple blood test that can detect heart- transplant rejection weeks or months earlier than previously possible.

The test relies on the detection of increasing amounts of the donor's DNA in the blood of the recipient, Stanford University researchers reported in the U.S. journal Science Translational Medicine.

The findings could potentially reduce the number of biopsies that transplant patients undergo, eventually replacing the risky procedure that involves removing heart muscle tissue for analysis, they said.

"This test appears to be safer, cheaper and more accurate than a heart biopsy, which is the current gold standard to detect and monitor heart-transplant rejection," senior author Stephen Quake, professor of bioengineering and of applied physics, said in a statement. "We believe it's likely to be very useful in the clinic. "

Transplant recipients with signs of rejection can be placed on anti-rejection medications to mitigate the immune system's attack. Sometimes, however, the rejection episode is too strong and a second transplant is required.

Currently, heart-transplant recipients undergo dozens of heart biopsies in the months and years after their transplant. The biopsies are uncomfortable and may cause complications such as heart rhythm abnormalities or valve damage. It's also expensive and time-consuming, and delivers results that can be subjective or can vary according to the sampling location within the heart.