Assessment of plasma neopterin in clinical kidney transplantation.

Serial plasma samples of 172 kidney transplant recipients and 42 chronic dialysis patients were evaluated retrospectively in a radioimmunoassay to determine the clinical relevance of plasma neopterin levels. Dialysis patients had a higher neopterin level 196 +/- 82 nmol/L (mean +/- SD) than 70 healthy controls (7 +/- 4 nmol/L). In 45 patients with a completely uneventful postoperative course, elevated pretransplant neopterin levels dropped rapidly within a week to a mean of 30 nmol/L and remained stable thereafter. In 22 outpatients with stable graft function there was a highly significant correlation between 170 paired serum creatinine and plasma neopterin values (r = 0.94). A group of 13 patients had experienced delayed graft function (ATN) without rejection. Their one-week mean neopterin level was 100 nmol/L and continued to drop in parallel with the serum creatinine. Another 15 patients rejected their kidneys irreversibly within 3 weeks-6 of them had extremely high neopterin levels during the rejection process (range 500-1000 nmol/L) that were not seen in other patients. A total of 169 rejection episodes in 43 patients were treated with bolus-dose cortisone. On the day of bolus therapy, both serum creatinine (P less than 0.002) and neopterin (P less than 0.005) were elevated. At 24 hours prior to bolus cortisone therapy, creatinine levels were not significantly elevated, whereas there was a significant rise in plasma neopterin (P less than 0.01). The overall sensitivity of neopterin increase was 86% with a 17% probability of false positives, and the sensitivity was 95% in biopsy-proved rejections. Plasma neopterin appears to be a useful marker for early detection of rejection and for identifying severe rejections that are not responsive to treatment.