Radioimmunoassay for urinary renal tubular antigen: a potential marker of tubular injury.

A human proximal renal tubular epithelial antigen (designated HRTE-1) was isolated and purified from a crude tubular preparation (Fx1A) by a process of salt fractionation, DEAE anion-exchange chromatography, and Sephadex G-200 gel filtration. Utilizing 125I-HRTE-1 and a rabbit antiserum specific for the proximal tubular brush border, as determined by immunofluorescent microscopy, a radioimmunoassay by competitive protein-binding was developed. HRTE-1 was demonstrated in serum and urine and in extracts of a variety of body organs. A range of concentrations for normal random urine samples and 24-hr urine excretion rates were determined. Random urine samples from 36 patients with a variety of functional and pathologic renal disorders were assayed for the HRTE-1 antigen. Twenty-three of 24 patients with either chronic nephropathy or pre-renal azotemia had normal urinary antigen concentrations, despite wide differences in urine flow rates, the degree of existing renal function, and the amount of proteinuria. Ten of 12 patients with acute tubular necrosis, however, had statistically abnormal HRTE-1 concentrations (high in eight patients, undetectable in two). These findings suggest that HRTE-1 antigen can be detected in both normal and pathologic urines, that altered antigen concentrations can be documented in at least one renal disorder, and that quantitation of HRTE-1 in urine may have clinical value as a marker of acute rubular injury.