Correlation between cystoscopic biopsy results and hypoamylasuria in bladder-drained pancreas transplants

Urinary amylase (UA) remains the most common biochemical parameter to detect rejection in bladder-drained pancreas allografts. With the development of the cystoscopic transduodenal pancreas transplant biopsy technique, tissue samples of the pancreas graft are now frequently obtained. A definitive correlative analysis between UA activity and biopsy results has not been done in the three different pancreas transplant categories (simultaneous pancreas-kidney, pancreas transplant alone, and pancreas after kidney).

We studied 66 pancreaticoduodenal biopsy specimens obtained for hypoamylasuria. Rejection was defined as a greater than 25% decrease from stable posttransplantation baseline on two consecutive measurements at least 12 hours apart. To perform biopsies we used our newly developed 14- and 16-gauge core-cut needles (50 cm long). Biopsy specimens were considered positive if either pancreatic or duodenal rejection was found. To assess the quality of UA activity we studied 13 biopsy specimens from patients with stable UA levels; these 13 specimens were negative for rejection.

Acute rejection was diagnosed in 36 biopsy specimens (55%). The mean decrease in UA levels was 67% +/- 8% (range, 28% to 99%) for the positive biopsy results, and 57% +/- 16% (range, 22% to 92%) for the negative biopsy results (p = 0.147). Within 1 month, UA levels returned to baseline in 19% of our patients with positive biopsy results versus 97% with negative results; postbiopsy 1-year graft survival was 64% versus 97% (p < or = 0.05). In assessing the test quality of our biopsy specimens (including 13 obtained for reasons other than hypoamylasuria), we found a sensitivity of 100% (stable UA levels mean no rejection) and a specificity of 30%. The predictive value of a positive test was 53%; of a negative test it was 100%. By performing biopsies we avoided antirejection treatment in 47% of the patients studied. We found no biopsy-related complications.

Stable UA levels reliably rule out rejection; a decrease is a marker for acute rejection but is unspecific. Performing biopsy is currently the only way to reliably diagnose rejection in solitary pancreas recipients (pancreas transplant alone and pancreas after kidney) and in simultaneous pancreas-kidney recipients with isolated hypoamylasuria. The procedure is safe and should always be attempted to avoid unnecessary rejection treatment.