This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidneys and Body Fluids, Subject name: Physiology
Which of the following provides the most accurate measure of GFR? 
Select and explain. 
A. Blood urea nitrogen (BUN), B. Endogenous creatinine clearance, C. Inulin clearance, D. PAH clearance
C: Inulin clearance
Answer: C: Inulin clearance 
Explanation: Ans. C. Inulin clearancea. Inulin clearance is the standard for measuring GFR.b. Because Inulin is neither secreted nor reabsorbed, only filtered, so rate of clearance is equal to GFR.c. (Creatinine is slightly secreted from the peritubular capillaries into the tubules)d. PAH clearance is used to measure renal plasma flow, not GFR.