Inulin is considered the gold-standard substance for measuring glomerular filtration rate because of which combination of properties?

• A Freely filtered, actively reabsorbed to completion in the proximal tubule
• B Freely filtered, completely secreted by the proximal tubule
• C Partially bound to plasma protein, freely filtered in its unbound form
• D Freely filtered, neither reabsorbed nor secreted by the tubules ✓

Explanation

Inulin is a small fructose polymer (about 5200 Da) that crosses the glomerular filter exactly like water, and the tubules neither reabsorb nor secrete it. Therefore its clearance equals GFR precisely. Creatinine, the practical alternative, is slightly secreted by the proximal tubule, so its clearance modestly overestimates GFR. PAH is both filtered and strongly secreted, making it a marker of renal plasma flow rather than GFR.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.