The finding, published this month in the journal Transplantation, is the result of a seven-year study of New Zealand, Australian and Swiss kidney transplant patients.
Once further testing is completed, it should mean the current test, an invasive biopsy procedure, could be replaced with a simple and accurate urine test, says study coordinator Dr Alex McLellan, of the University’s Department of Microbiology and Immunology.
He says that although the idea was first tested in 2002, proof that the test could be used to monitor the effectiveness of renal transplants “required years of patient sample collection and research into a molecule present in the urine.”
“The main challenge facing transplant physicians is the host’s immune system, which sees the graft as foreign and attacks the transplanted organ. Keeping the transplanted organ alive and functioning in the host requires potent immunosuppressive drugs, which must be taken for the person’s life,” Dr McLellan says.
“Detecting transplant rejection at the earliest possible time is essential to prevent transplant loss because it allows immediate intervention with additional immunosuppressive drugs.”
This is important given that four out of every 120 New Zealanders will lose their kidney transplant within the first year, he says.
The newly developed urine test detects one of the molecules (called Major Histocompatibility Complex (MHC) molecules) that are released from the kidneys into urine during transplant rejection.
In the study, the urine levels of MHC molecules soared during transplant rejection, and could be detected days before confirmation of rejection using the standard biopsy method. They found that these patients who tested positive for MHC in their urine had a greater than 90 per cent chance of suffering transplant rejection.
“The kidney biopsy is still the most reliable method to date for diagnosing transplant rejection but is invasive. The urine test is rapid, simple and non-invasive, requiring basic materials to detect a molecule released into urine during transplant rejection,” Dr McLellan says.
Dr McLellan hopes the test, which is unlikely to become available for some years until further testing on larger groups of kidney transplant patients has been done, will improve diagnostic monitoring during the post-transplant hospitalisation of patients. It would also be valuable to patients at home as a urine dip-stick test for long-term monitoring of transplant status.
Dunedin Hospital Transplant Specialist Professor Rob Walker, who was also part of the research team, says the use of urinary biomarkers is “a relatively new area with great potential.”
“A transplant rejection, if not detected early, will lead to kidney injury which in the worst case scenario would lead to the loss of the transplanted kidney,” Dr Walker says.
“Early detection allows prompt treatment to preserve kidney function.”
Dr Alex McLellan
Department of Microbiology and Immunology
Tel 64 3 479 7728 (or 64 3 479 7147)