Serum hippuric acid concentration in renal allograft rejection, ureter obstruction, and tubular necrosis.

Plasma from 35 renal allograft recipients (21 males and 14 females) was sampled daily and analyzed for hippuric acid (HA) by high-performance liquid chromatography (HPLC) and serum creatinine. Twelve of these patients experienced an acute renal allograft rejection or a ureter obstruction as proven by clinical signs and biopsy, as well as by radiography or ultrasound, respectively. Two patients suffered from tubular necrosis followed by rejection during the postoperative period. Mean serum HA increased by 39.9 mumol/l from baseline (range 20.4-115.5 mumol/l) in patients with acute rejection 3 days after an initial increase that was observed 24 h before the mean serum creatinine increased by 107.1 mumol/l (range 21-193 mumol/l). In cases of ureter obstruction, HA rose by 1.6 mumol/l (range 1-8.2 mumol/l), significantly less than elevations due to rejection. The increase in creatinine, however, amounted to 65.3 mumol/l (range 22-140 mumol/l) and was not different from the change in rejecting patients. Successful antirejection treatment coincided with a decrease in serum HA starting 24 h earlier than the decrease in the serum creatinine concentration. Of special interest was the observation of a parallel decrease in HA with creatinine concentration in patients with tubular necrosis after allotransplantation; HA increased in cases of an additional rejection. Our data suggest that HA, which is excreted by tubular secretion and glomerular filtration, could be a sensitive and early marker of acute allograft rejection. Furthermore, it seems to discriminate between acute renal allograft rejection and ureter obstruction. It might, therefore, be of value in the diagnosis of rejection complicating tubular necrosis after transplantation.