Determination of Inulin and p-Aminohippurate Clearances without Urine Collection

Standard inulin and PAH clearances utilizing blood and urine collections were determined in 50 individuals with chronic kidney disease. Each of these patients, as well as 14 anephric patients, also had a bolus infusion of inulin and p-aminohippurate (PAH). ‘Bolus clearances’ were derived from the disappearance slope of their blood concentrations. The bolus clearances of inulin and PAH correlated well with the standard technique. However, the bolus PAH clearance consistently overestimated the standard method. This overestimate was significant and defined by a regression factor. In the anephric patients the bolus PAH clearances were 104 ± 83 and 63 ± 33 ml/min utilizing 30- to 45-min and 45- to 60-min blood samples; the bolus inulin clearances were 18 ± 13 and 6 ± 6 ml/min utilizing 60- to 90-min and 90- to 120-min blood samples. The data suggest either an appreciable extrarenal excretion and/or metabolic alteration of PAH during the bolus study. Inulin appears to be excreted essentially by the kidneys alone.