Glomerular filtration rate by single-injection inulin clearance: definition of a workable protocol for children

Abstract

The total serum clearance of inulin after a single intravenous injection is an established method for the determination of the glomerular filtration rate (GFR). To optimize this procedure in children, we analysed 117 serum inulin time-decay curves in 59 children (age range 1·3-15·2 years) with renal disease. It was found that the two-compartment model fitted statistically better to the disappearance curves of serum inulin than the one-compartment model. The sampling frequency could be reduced from 12 to a minimum of seven data points (t = 0, 10, 20, 30, 65, 120 and 240 min) in 4 h without a relevant change in the fit of the two-compartment model to the data or in the calculated clearance of serum inulin. We conclude that, by using a standardized 'seven-sample schedule', followed by a two-compartment analysis, the single-injection serum clearance of inulin is a suitable compromise between practical convenience and clinical accuracy for the determination of the GFR in children.