Inulin is considered the gold standard substance for measuring GFR. Which set of properties makes it ideal?
- A Freely filtered, neither reabsorbed nor secreted anywhere along the nephron, not metabolized by the kidney ✓
- B Freely filtered, partially reabsorbed in the proximal tubule, not secreted
- C Freely filtered, secreted by the organic anion transporters in the proximal tubule
- D Freely filtered, completely reabsorbed so that its urinary concentration reflects tubular transport capacity
Correct answer: A. Freely filtered, neither reabsorbed nor secreted anywhere along the nephron, not metabolized by the kidney
Explanation
Inulin's clearance equals GFR precisely because its urinary excretion rate arises solely from filtration: it is freely filtered at the glomerulus and undergoes no reabsorption, secretion, synthesis, or degradation anywhere in the nephron. Creatinine fails this standard because it is secreted by the proximal tubule, which inflates its clearance above the true GFR.
Reference: Vander's Renal Physiology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.