After surviving the agonizing wait for a new heart and a grueling transplant operation, recipients of a donated heart face another major battle: avoiding the body’s rejection of the new organ.

Rejection can cause the heart to fail, requiring another transplant to keep the patient alive.

Stanford University scientists are working to perfect a new tool they say will help monitor patients for signs of rejection. A test that identifies pieces of D-N-A from the donated heart that are floating freely within the recipient’s blood will help show doctors whether rejection is occurring.

Rejection happens when the recipient’s immune system sees the new heart as an intruder that could do harm and attacks it. D-N-A breaks off the heart in little pieces, which then circulate through the blood. A certain level of donor D-N-A in the bloodstream indicates rejection.

The scientists say pinpointing the D-N-A and measuring how much there is can reveal when rejection is occurring.

They have conducted several tests of the new screening tool and say hundreds of blood samples from 65 patients have shown them the threshold that signals rejection.

A simple blood test to check for rejection would be a welcome development for heart transplant patients. Currently, the most reliable way to monitor for this dire complication is through regular heart biopsies.

In addition to being uncomfortable, heart biopsies are risky and expensive. The researchers also said their new blood test may be able to predict organ rejection before it occurs.

Swapping biopsies for blood tests and having a reliable predictor of rejection would make the lives of heart transplant patients easier. With all they’ve been through, these brave people deserve a break.