NEW YORK (Reuters Health) - The renal arterial resistance index, determined with ultrasound, and DNA microarray profiling appear to be useful in predicting graft survival after kidney transplantation, according to findings from two studies published in the July 10th issue of The New England Journal of Medicine.

"For the short term, predicting outcomes after transplantation is not as important as it once was, since greater than 90% of renal allografts now survive for at least 1 year," Dr. Philip A. Marsden of the University of Toronto, author of a related editorial, told Reuters Health. "But in the long term, there still remains a strong chance of graft loss," he added. The ability to predict future graft loss is important in guiding therapeutic interventions, Dr. Marsden said. "The current studies provide some interesting new and old tools for predicting outcomes after transplantation."

In the first study, Dr. Jorg Radermacher, from Hannover Medical School in Germany, and colleagues used Doppler ultrasound to measure the renal arterial resistance index in 601 patients who underwent renal transplantation between August 1997 and November 1998.

Testing was performed in all patients at least 3 months after transplantation. An index of 80 or higher was considered abnormally high. The patients were followed for at least 3 years.

Twenty percent of patients had an abnormally high resistance index. An abnormally high index was tied to a 50% or greater drop in creatinine clearance and to an increased risk of requiring dialysis--the indicator for graft failure (p < 0.001). Moreover, the mortality for patients with an elevated index was 30%, compared with a rate of only 7% for patients with lower values.

On multivariate analysis, patients with a high resistance index were 9.1-times more likely to lose their allograft than were patients with lower values, the investigators note.

In the second study, which included pediatric transplant recipients, Dr. Minnie Sarwal and colleagues, from Stanford University in California, evaluated gene-expression patterns that could predict renal allograft loss.

Despite having similar appearances on light microscopy, biopsy samples from rejected kidneys often varied greatly in their gene-expression patterns. Analysis of the patterns revealed that there were at least three subtypes of acute rejection. In particular, the authors identified a B-cell molecular pattern that was strongly tied to steroid resistance and to severe graft rejection.

"The study by Dr. Radermacher's team provides us with startling new information that a commonly used test in clinical medicine is a very powerful predictor of long-term graft function," Dr. Marsden said. "In contrast, the second study provides us with a relatively new technique that predicts graft loss."

The ultimate goal is to achieve complete engraftment of transplanted organs, Dr. Marsden noted. "Now that we have some predictors for transplant outcomes, further studies are needed to shed light on what makes grafts fail and what can be done to prevent it."

N Engl J Med. 2003 Jul 10;349(2):115-24

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