Measurement of renal function without urine collection. A critical evaluation of the constant-infusion technic for determination of inulin and para-aminohippurate.

Abstract

Abstract The assessment of renal function in infants and children is made difficult by problems in obtaining complete urine collections. The traditional and the constant-infusion methods of determining inulin and paraaminohippurate clearance were compared in 61 patients, 32 of whom had a variety of renal diseases. Glomerular filtration rates ranged from 1.6 to 133 ml per minute. Values for inulin clearance by the two methods correlated closely (r equal to 0.993) at all levels of renal function and in the presence or absence of edema. Inulin clearance by the constant-infusion technic averaged 103.2 per cent of clearance. Correlation between the two methods of measuring para-aminohippurate clearance was r equal to 0.971, but values by the infusion method averaged 21.8 per cent above true clearance, presumably owing to extrarenal excretion of para-aminohippurate. The estimation of glomerular filtration rate by the technic of constant inulin infusion constitutes a simple, accurate and reproducible meth...