<prompt> Ideal substance for measuring GFR should have the following characteristics EXCEPT:Should be secreted in tubulesShould be nontoxicShould not remain in the bodyShould not be protein bound  <response>: Ans. a Should be secreted in tubules. Ref. Ganong, Physiology, 21stpg.709GLOMERULAR FILTRATION RATE GFRCharacteristics of a substance suitable for measuring the GFR, by determining its clearance:1. Freely filtered i.e., not bound to protein in plasma or sieved in the process of ultrafiltration.2. Not reabsorbed or secreted by tubules.3. Not metabolized.4. Not stored in kidneys.5. Not toxic.6. No effect on filtration rate.7. Preferably easy to measure in plasma and urine.Inulin is freely filtered and is neither reabsorbed nor secreted.GFR by definition is net volume of plasma from which a substance is cleared completely per unit time.GFR UVPWhere U -- concentration in urineV -- volume of urine passedminuteP -- concentration in plasma.Clinically, creatinine clearance is good measure of GFR. 