Para-aminohippurate
Aminohippuric acid or ''para''-aminohippuric acid (PAH), a derivative of hippuric acid, is a diagnostic agent useful in medical tests involving the kidney used in the measurement of renal plasma flow. It is an amide derivative of the amino acid ...
(PAH) clearance is a method used in
renal physiology
Renal physiology (Latin ''rēnēs'', "kidneys") is the study of the physiology of the kidney. This encompasses all functions of the kidney, including maintenance of acid-base balance; regulation of fluid balance; regulation of sodium, potassium, ...
to measure
renal plasma flow, which is a measure of
renal function.
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:
:
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.
Precision
The renal
extraction ratio of PAH in a normal individual is approximately 0.92,
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.
See also
*
Renal blood flow
In the physiology of the kidney, renal blood flow (RBF) is the volume of blood delivered to the kidneys per unit time. In humans, the kidneys together receive roughly 25% of cardiac output, amounting to 1.2 - 1.3 L/min in a 70-kg adult male.
It ...
References
External links
Renal Clearance Techniques
{{DEFAULTSORT:Pah Clearance
Renal physiology
Blood tests