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Capillary electrophoresis method to measure p-aminohippuric acid in urine and plasma for the assessment of renal plasma flow.

p -Aminohippuric acid (PAH), a derivative of aminobenzoic acid, is almost completely extracted from the blood after a single passage by the kidney through a combination of glomerular filtration and proximal tubular secretion. On the basis of these properties, the renal clearance of intravenously administered PAH has been used as a measure of renal plasma flow (RPF) (1). PAH remains the “gold standard” for the noninvasive measurement of RPF in patients and study participants and may be useful for assessing the effect of disease states or pharmacologic agents on renal function.

The standard method for PAH measurement is a colorimetric assay of a diazotation reaction that is labor-intensive (2)(3). Because of the complexities of the standard colorimetric PAH assay, its measurement has often been confined to research or used only in specialized laboratories. Measurement of PAH in urine and plasma by HPLC has been described (4)(5)(6)(7), but it requires relatively large sample volumes and time-consuming extraction procedures. We recently found that capillary electrophoresis (CE) is an efficient, inexpensive, and reliable method for measurement of the nonradiolabeled iothalamate in urine and plasma samples for the assessment of glomerular filtration rate (8)(9). Analysis by CE is analytically faster than standard HPLC or colorimetric assays, requires less reagent preparation and smaller sample size, minimizes drug interferences, and improves test turnaround time. With the development of a method for PAH on CE, assays for both RPF and glomerular filtration rate could also be obtained with a single methodology. This report describes a new quantitative CE assay for PAH in urine and plasma and compares it with the standard colorimetric assay.

PAH was measured by CE on a Beckman Pace instrument using Beckman System Gold software, 50 mmol/L borate buffer (pH 10.2), ultraviolet detection at …