This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidneys and Body Fluids, Subject name: Physiology
[{'content': 'Ideal substance for measuring GFR should have the following characteristics EXCEPT: \nSelect and explain. \nA. Should be secreted in tubules, B. Should be nontoxic, C. Should not remain in the body, D. Should not be protein bound', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a (Should be secreted in tubules). (Ref. Ganong, Physiology, 21st/pg.709)GLOMERULAR FILTRATION RATE (GFR)Characteristics 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 passed/minuteP -- concentration in plasma.Clinically, creatinine clearance is good measure of GFR.', 'role': 'assistant'}]