<prompt> Filtration fraction can be best determined by:Inulin and mannitolPAH and InulinInulin and creatininePAH and mannitol  <response>: To calculate the filtration fraction, which is the fraction of plasma that filters through the glomerular membrane, one must first know the RPF PAH clearance and the GFR inulin clearance. FILTRATION FRACTION GFRinulin clearanceRPFPAH clearance Inulin and mannitol measure ECF volume Inulin and creatinine both measures GFR, but creatinine is secreted in the tubules hence GFR estimated by creatinine is falsely higher. 