PAH-Clearance

The PAH clearance ( CPAH; short for para- aminohippuric acid clearance or p- aminohippuric acid clearance) is a medical parameter for the assessment of renal function. He describes the volume of blood plasma, which rid the kidneys per unit time of para- amino hippuric acid (PAH ) excretion by. The PAH clearance is used for the determination of renal blood flow and thus is used to assess renal function. PAH - clearance is typically about 550-720 ml/min/1, 73 m². Since this method for the determination of renal clearance is quite expensive, it is used only for scientific questions. Today one uses rather the MAG3 clearance ( mercaptoacetyltriglycine ), see also Nierenszintigrafie.

Implementation and computation

P- aminohippuric acid is infused as a sodium salt. At low plasma concentrations of the substance is almost completely excreted during passage of blood through the kidneys into the urine. This is accomplished by glomerular filtration (20-30%) and tubular secretion (70%):

Wherein UPAH pPAH and the p- aminohippuric acid levels in urine and blood plasma, and V is the Harnzeitvolumen. Since approximately 90% of p- aminohippuric acid are excreted by the kidneys in the urine, the PAH clearance must be divided by 0.9 to calculate the renal plasma flow (RPF). Taking into account the hematocrit ( Hct ) of the renal blood flow can be calculated from the renal plasma flow: RBF = RPF / (1- Hct ).