Urinary protein markers of tubulointerstitial nephritis.

In an effort to identify new diagnostic features of tubulointerstitial nephritis (TIN), urinary total protein concentrations and urinary excretion rates of four serum proteins and of proximal renal tubular epithelial antigens were determined for five normal subjects and for 44 patients with well-characterized renal diseases. Four urinary protein indices correlated with TIN: clearance of lysozyme/clearance of albumin > 20; clearance of immunoglobulin G/clearance of albumin % > 55 per cent; renal tubular epithelial antigen excretion > 10 units per min; urinary albumin/urinary total protein concentrations < 50 per cent. Of TIN patients, 86 per cent were (+) to one or more of these criteria whereas 89 per cent of glomerular disease patients were (-) to all criteria. By combining these criteria into multiphasic testing profiles, 88 per cent of patients could be successfully categorized as having either tubulointerstitial or glomerulonephritis. This finding suggests the potential diagnostic value of these new testing parameters.