Best test for GFR is with:

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 (standard)Q- Neither reabsorbed, nor secreted by tubules- Creatinine- Nontoxic - Not metabolized by body.