Testing for molecular markers in the urine of kidney transplant patients could reveal whether the transplant is failing and why, according to a recent research.

Transplants are life-saving treatments for patients with end-stage kidney disease but around 25 percent fail within five years, either because the body begins to reject the new organ, or because a viral infection has taken hold of the kidney. The two problems require diametrically opposite treatments but often, by the time the cause of the failure is confirmed, it is too late to prevent it.

The new research, presented at the 27th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID), suggests that the two problems could be distinguished from each other via the detection of cocktail of proteins shed from the kidney into the patient's urine. The research could form the basis of a urine test to pick up early signs of transplant failure and ensure the correct treatment is given.

Presenter Ibai Los-Arcos from the Hospital Universitari Vall d'Hebron, Barcelona, Spain explained: "Kidney transplant patients are given immune suppressing drugs to prevent their bodies from rejecting the donor organ, but this is a balancing act. If treatment is insufficient, the organ can be destroyed by the immune system. On the other hand, too much suppression can allow an infection to take hold. Often by the time we know which is happening, it's too late to save the organ."

The study focused on a virus called BK. The BK virus causes a common infection which most people experience during childhood mainly with no symptoms. Following infection the virus remains in the body, lying dormant in the kidneys and urinary tract. However, when transplant patients are given immune suppressing drugs, the virus can reactivate, infecting and destroying the new kidney. This usually happens within two years of the transplant.

The research was a pilot study in four Spanish hospitals involving 30 kidney transplant patients. Ten of the patients had been diagnosed with T-cell mediated acute rejection (TCMR), meaning the kidney was being rejected. Another ten had been diagnosed with BK virus nephropathy, meaning the virus was destroying the kidney. The other ten patients had no known problems with their transplanted kidneys (stable graft).

The team analysed urine samples from each patient to find out which proteins were present. Most of the proteins they found are known to come from the human body. However, in those with the viral infection, they were able to detect proteins that are known to come from the BK virus. These were not found in samples from patients with TCMR or with a stable graft.

When they looked more closely at the human proteins, the researchers also found that they could use the levels of those proteins to differentiate between patients who had TCMR, BK virus nephropathy or a stable graft.

Los-Arcos told the congress: "If we can confirm these results in a prospective validated cohort of patients, we may be able to develop a urine test to indicate when a kidney transplant is failing and at a much earlier stage. More importantly, it would be able to differentiate whether it is failing because of the BK virus or because of organ rejection. If that's the case, we will be able to choose the correct treatment to address the problem and hopefully have more successful kidney transplantations.