The US Food and Drug Administration announced that it has cleared for marketing a non-invasive test that uses molecular expression techniques to assist doctors in managing heart transplant patients post-surgery for potential organ rejection.

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

AlloMap measures genetic information contained in the white blood cells (cells of the immune system that defend the body against invading viruses, bacteria or other foreign material) from a patient's blood sample.

Specifically the test measures gene expression or how DNA transcribes its genetic instructions to RNA, the nucleic acid that translates and carries out those instructions of 20 different genes, resulting in a score that indicates whether a heart transplant patient is unlikely to be rejecting the new organ.

Nearly every cell of the body contains a full set of chromosomes and identical genes but only a fraction of these genes are turned on or expressed in any given cell. Gene expression occurs when certain molecular information contained within DNA is transcribed to create molecules known as RNA. These molecules in turn make the proteins that perform most of the critical functions of cells.

Following a heart transplant, physicians regularly monitor patients for transplant rejection, a significant risk to patient survival. Rejection occurs when the patient's immune system fails to accept the new organ and begins to attack it. Successful heart transplants depend on a balanced immune system response a response that is suppressed enough to accept the new organ but strong enough to protect the patient from infections.

Clinicians often rely on heart biopsy to gauge whether a patient is rejecting the transplanted heart. 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 happen during the first six weeks after surgery and 25 per cent of patients have signs of possible rejection at least once during the first year following a transplant.

XDx Inc developed AlloMap using blood and biopsy samples and other information collected from heart transplant recipients at nine U S heart transplants centres participating in the Cardiac Allograft Rejection Gene expression Observational study (CARGO). CARGO provided data from 153 patients on 300 medical visits at various times after heart transplant study.

AlloMap is the third in vitro diagnostic multivariate index assay (IVDMIA) cleared by the FDA. IVDMIAs are medical devices that combine the values of multiple variables to yield a single, patient-specific result.