<prompt> Best test for GFR is with:InulinHippuric acidCreatininePAH  <response>: A i.e. Inulin Measurement of GFRGFR can be measured by measuring the excretion plasma level of a substance that is freely filtered through glomeruli and neither secreted not reabsorbed by the tubulesQ.Requirement of substances used to measure GFR- Substances used- Filtered freely- Inulin standardQ- Neither reabsorbed, nor secreted by tubules- Creatinine- Nontoxic - Not metabolized by body. 