In CKD stage 3 (GFR ~30 mL/min) with a drug renally cleared having baseline renal CL of 4 L/h in healthy GFR ~120 mL/min, estimate CLrenal in CKD stage 3.

• A. 1.0 L/h
• B. 2.0 L/h
• C. 4.0 L/h
• D. 0.25 L/h

Answer: (A)

Renal clearance for a drug cleared mainly by the kidneys scales with GFR when other renal processes stay the same. If GFR falls from about 120 mL/min to about 30 mL/min, that’s a quarter of normal. Starting from a healthy renal clearance of 4 L/h, multiply by 30/120 (0.25): 4 × 0.25 = 1 L/h. So, in CKD stage 3, CLrenal is about 1 L/h.