<unk>  is a measure in renal physiology, primarily used to calculate renal plasma flow in order to evaluate renal function. It measures the percentage of the compound entering the kidney that was excreted into the final urine. Measured in concentration in blood plasma, it may thus be expressed as: : , where Pa is the concentration in renal artery, and Pv is the concentration in the renal vein. For instance, para aminohippuric acid (PAH) is almost completely excreted in the final urine, and thus almost none is found in the venous return (Pv ~0). Therefore, the<unk>  of PAH ~1. This is why PAH is used in PAH clearance to estimate renal plasma flow.
Extraction ratio
Surface probability
Form constant
Frequency following response
Time-activity curve
Peak kilovoltage
E/A ratio
Base curve radius