This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Substance used to measure renal perfusion:March 2007 
Select and explain. 
A. lnulin, B. PAH, C. Creatinine, D. Mannitol
B: PAH
Answer: B: PAH 
Explanation: Ans. B: PAHPara-Aminohippurate (PAH) is a substance used in the measurement of renal blood flow.It is useful in this measurement because it is primarily secreted by the renal tubules; only 20% is filtered by the glomerulus. The renal extraction ratio of PAH is a normal individual is approximately 0.92.