PAH clearance

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Para aminohippurate clearance or PAH clearance is a method used in renal physiology to measure renal plasma flow, which, in turn, is a measure of renal function.

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

$RPF = \frac{U_{PAH}}{P_{PAH}} V$

What in fact 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.

[edit] Precision

The renal extraction ratio of PAH in a normal individual is approximately 0.92^[1], and thus not exactly 1.0. Thus, this method usually underestimates RPF by approximately 10%. This margin of error is generally acceptable considering the ease with which eRPF is measured.

[edit] References

^ Reubi FC. Glomberular Filtration Rate, Renal Blood Flow and Blood Viscosity during and after Diabetic Coma. Circ. Res. 1953;1;410-413. Available at: http://circres.ahajournals.org/cgi/reprint/1/5/410.pdf. Accessed on: May 2, 2007.

v • d • e Urinary system, physiology: renal physiology and acid base physiology

Filtration	Renal blood flow - Ultrafiltration - Countercurrent exchange

Hormones affecting filtration	Antidiuretic hormone (ADH) - Aldosterone - Atrial natriuretic peptide

Secretion/clearance	Pharmacokinetics - Clearance of medications

Reabsorption	Solvent drag -Na⁺ - Cl^- -urea -glucose -oligopeptides -protein

Endocrine	Renin - Erythropoietin (EPO) - Calcitriol (Active vitamin D) - Prostaglandins

Assessing Renal function / Measures of dialysis	Glomerular filtration rate - Creatinine clearance - Renal clearance ratio - Urea reduction ratio - Kt/V - Standardized Kt/V - Hemodialysis product - PAH clearance (Effective renal plasma flow - Extraction ratio)

Acid base physiology	Fluid balance - Darrow Yannet diagram - Body water - Interstitial fluid - Extracellular fluid - Intracellular fluid/Cytosol - Plasma - Transcellular fluid - Base excess - Davenport diagram - Anion gap - Arterial blood gas

Buffering/compensation	Bicarbonate buffering system - Respiratory compensation - Renal compensation