The use of sodium para-aminohippurate (PAH) as a marker of the completeness of urine collections: Studies in patients receiving total parenteral nutrition

Abstract

The completeness of 32 urine collections obtained from 12 patients receiving total parenteral nutrition continuously over 24 h periods was assessed by adding 750 mg and 2 μCi (74 kBq) of 14C sodium para-aminohippurate monohydrate (PAH) to their infusate and measuring the recovery of these markers in urine. The recovery was found to be 73 ± 3% (SEM) of the administered dose of PAH (in contrast to complete recovery of the marker in normal subjects given a bolus injection). Measurements of nitrogen, calcium and phosphorus in urine samples of the parenterally fed patients, and their calculated balances, were substantially in error. Creatinine excretion expressed as a percentage of the predicted value, varied by as much as 30% for a given degree of PAH excretion. Radionuclide measurements of urinary PAH were compared with colorimetric and chromatographic measurements. Some drugs and their urinary metabolites interfered with the colorimetric measurements, whilst other urinary compounds interfered with the chromatographic measurements. It is suggested that PAH, particularly labelled PAH, is useful for assessing the completeness of urine collections especially in parenterally fed patients participating in metabolic or nutritional studies.