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
The best test for GFR is with 
Select and explain. 
A. Inulin, B. Hippuric acid, C. Creatinine, D. PAH
A: Inulin
Answer: A: Inulin 
Explanation: Properties of Inulin
-        Easily filtered by kidney
-        Not absorbed by kidney
-        Not secreted by kidney
-        Not metabolized by kidney
-        Not synthesized by kidney
-        Non-toxic
-        Easily measurable
Thus it is the best substance to use for measurement of GFR.