Glomerular and tubular function in non-oliguric acute renal failure.

Glomerular and tubular function were evaluated in 30 non-oliguric patients with increasing azotemia following open heart surgery. Fractional clearances (theta) of test solutes relative to that of inulin were determined. In 16 patients, theta dextran (radius 22 to 30 A) exceeded unity, a finding attributed to inulin backleak through necrotic tubules. These patients were classified as having acute renal failure; 14 subsequently required dialysis. In the remaining patients (N = 14), theta dextran was normal. These patients were considered to have prerenal failure; all recovered spontaneously. clearance of inulin (Cin) was lower in acute renal failure than in prerenal failure (12 +/- 2 versus 18 +/- 2 ml/min/1.73 m2; p less than 0.025). The apparent difference in glomerular filtration rate when Cin is used as an index was abolished, however, when Cin in acute renal failure was corrected for tubule backleak of inulin. In acute renal failure, fractional clearance of p-aminohippurate (theta PAH) was 7.1 +/- 1.0, and fractional excretion of potassium (FEk) was 160 +/- 18 percent. These findings strongly suggest that secretory ability in both proximal and terminal tubule augments, respectively, is preserved in acute renal failure. Compared with prerenal failure, the urine-to-plasma inulin ratio was lower (U/Pin = 10 +/- 1 versus 25 +/- 4; p less than 0.005) and FENa was higher (FENa = 5.1 +/- 1.5 versus 0.5 +/- 1.0 percent; p less than 0.01) in acute renal failure.