Rapid radioimmunoassay for diagnosing acute tubular necrosis

A previously described method for recovering a proximal renal tubular epitheal antigen (HRTE-1) from normal human kidney was modified by using ion-exchange and immunoaffinity chromatography in order to create easily reproducible conditions for antigen isolation. Radioiodinated HRTE-1 was then used to establish a 3-hour, double-antibody radioimmunoassay (RIA) for the purpose of testing whether the urinary excretion of this antigen might seve as a useful marker of acute tubular necrosis (ATN). Urines from 51 patients (ATN, 22: chronic nephropathies, 24; prerenal azotemia, 5) and from 36 normal subjects were assayed for HRTE-1. 79% of ATN patients had abnormal antigen concentrations while 100% of all other urines had urine antigen concentrations within a previously established range for random normal urine samples. When used as a differential diagnostic test of either ATN versus chronic nephropathies, or of ATN versus prerenal azotemia, 90 and 81% discrimination was achieved, respectively. The majority of ATN and prerenal azotemia patients presenting with atypical conventional diagnostic parameters (urine Na, urine osmolality, urine sediment, fractional Na excretion) were correctly diagnosed by RIA. Further study of HRTE-1 excretion in acute and chronic renal diseases seems indicated, both to elucidate pathophysiologic mechanisms and to determine whether HRTE-1 is a clinically useful marker of ATN.