Creatinine excretion rates for evaluation of kidney function in children.

A protein load protocol for evaluation of kidney function was tested in normal children and pediatric renal patients. An overnight, timed urine collection was used for calculation of the baseline creatinine clearance and creatinine excretion rate. One hour following ingestion of a standardized protein meal (baked chicken), a 2-3 h urine collection was begun. The post-protein meal changes in creatinine clearance showed considerable variation in both the normal children and those with renal disorders. In contrast, the rate of excretion of creatinine was consistently increased in the normal children following the protein meal (73.4 +/- 18%; range 48.2%-122.4%). Of 33 renal patients, 14 showed less than a 48% increase in creatinine excretion rate, even though 9 of these children had baseline creatinine clearances within the normal range. These 9 patients have evidence of less than normal quantities of functioning renal tissue. Serial studies over a year on 2 children who presented with acute renal failure showed a progressive increase in creatinine clearance with scant increases in creatinine excretion rate. These studies provide indirect evidence that a less than normal enhancement of the rate of creatinine excretion following a protein load reflects the presence of adaptive glomerular hyperfiltration and hyperperfusion.