Renal clearance physiology - GFR vs effective renal plasma flow markers (inulin vs PAH)
Core concept
- Clearance = volume of plasma completely cleared of a substance per unit time
- Cx = (Ux x V) / Px
- What a marker measures depends on how the tubule handles it
| Handling | Clearance equals | Marker |
|---|---|---|
| Filtered only, not secreted or reabsorbed | GFR | Inulin (gold standard), iohexol, 51Cr-EDTA, 99mTc-DTPA |
| Filtered and secreted, ~100% extracted in one pass | Effective renal plasma flow | PAH |
| Filtered and reabsorbed | < GFR | Glucose, urea, Na |
- Inulin -> GFR ~120 mL/min. PAH -> ERPF ~600 mL/min
- Filtration fraction = GFR / RPF = ~0.2 (20%)
- PAH extraction ~90% -> ERPF underestimates true RPF by ~10%
- RBF = RPF / (1 - Hct) -> ~1100 mL/min = ~20-25% of cardiac output
3 more sections, plus exam facts
Premium unlocks every note across every specialty, and the full exam fact library behind it.
Get premium access