Early detection of aminoglycoside nephrotoxicity with urinary beta-2-microglobulin

The authors used a radioimmunoassay to evaluate the changes in the urinary excretion of β2-microglobulin (β₂M)in 21 patients receiving aminoglycosides for treatment of infection. Excretion of this protein rose to a peak at least 5 times the baseline value in the urine, and declined rapidly to control values after drug administration ceased. In six patients who developed aminoglycoside nephrotoxicity, urinary β₂M excretion rose 5 days or more before serum creatinine rose, and 5 of 6 nephrotoxic patients excreted more thean 50 mg/day (normal, <0.1 mg/day). Urinary β₂M is a non-specific indication of renal tubular damage, but heralds aminoglycoside-induced damage before standard tests of kidney function change.