PAH clearance

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| name = PAH clearance

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| purpose =measure renal plasma flow

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Para-aminohippurate (PAH) clearance is a method used in renal physiology to measure renal plasma flow, which is a measure of renal function.{{citation needed|date=January 2020}}

PAH is completely removed from blood that passes through the kidneys (PAH undergoes both glomerular filtration and tubular secretion), and therefore the rate at which the kidneys can clear PAH from the blood reflects total renal plasma flow.

The concentration of PAH is measured in one arterial blood sample (P_PAH) and one urine sample(U_PAH). The urine flow (V) is also measured. Renal perfusion flow is then calculated by:

:$RPF\; =\; \backslash frac\{U\_\{PAH\}\}\{P\_\{PAH\}\}\; V$

What is calculated is the effective renal plasma flow (eRPF). However, since the renal extraction ratio of PAH almost equals 1, then eRPF almost equals RPF.