Diagnosis of Renal Proximal Tubular Injury by Urinary Immunoassay for a Proximal Tubular Antigen, the Adenosine Deaminase Binding Protein

A sandwich ELISA assay has been formatted from two commercially available murine monoclonal antibodies, URO-4 and URO-4a, directed against a 120,000 dalton glycoprotein, the adenosine deaminase binding protein (ABP), found on the brush border of the renal proximal tubular epithelial cell. Untimed urine samples from 37 normal individuals and urinary ABP less than 0.1 AU; 37 patients with pure glomerular disease had ABP less than 0.4 AU (with 29, or 76% less than 0.2 AU); 10 patients with pre-renal azotaemia had ABP less than 0.6 (with 8, or 80% less than 0.3 AU). In contrast, 79 patients with post-ischaemic acute tubular necrosis had ABP greater than 0.6 AU. Acute renal failure due to myoglobinuria, contrast dye, and aminoglycoside toxicity were all associated with urinary ABP greater than 1.0 AU. In addition, all six patients with acute bacteraemic pyelonephritis had ABP greater than 0.7 AU, as opposed to ABP less than 0.2 AU in the urines of 12 women with acute cystitis. We conclude that this monoclonal antibody based urinary assay is a sensitive measure of renal proximal tubular injury, reliably distinguishes acute tubular from glomerular disease, and may be helpful in differentiating forms of urinary tract infection.