Short-term protein loading in assessment of patients with renal disease.

The effect of short-term protein loading on the glomerular filtration rate in normal persons and patients with renal disease was evaluated. Previous studies have demonstrated that in healthy subjects, protein loading results in an increased glomerular filtration rate. By determining the glomerular filtration rate preceding (baseline glomerular filtration rate) and following (test glomerular filtration rate) oral protein loading, it was possible to define (1) the filtration capacity (test glomerular filtration rate) and (2) the renal reserve (test glomerular filtration rate - baseline glomerular filtration rate) of the kidney. In normal persons, filtration capacity averaged 157 +/- 13 ml per minute and renal reserve 34 ml per minute. The test glomerular filtration rate was reproducible and independent of protein intake, whereas baseline glomerular filtration rate was significantly influenced by diet. Patients with renal disease were found to have a reduced renal reserve and/or a diminished filtration capacity. The reduction in filtration capacity appears to correlate with the damage sustained by the organ. It is suggested that an abnormal response to protein loading in renal disease may herald the fall in the baseline glomerular filtration rate and the rise in plasma creatinine level.