PEBC MCQ Pharmaceutical Calculations question: age x weight kg x (2)

PEBC MCQPharmaceutical Calculations

HN is an 80 year old female weighing 55 kg with a serum creatinine of 110 umol/L. Using CrCl (mL/min) = [(140 - age) x weight (kg) x 1.23] / SCr (umol/L), multiplied by 0.85 for females, what is HN's estimated creatinine clearance?

a. 31 mL/min
b. 37 mL/min
c. 43 mL/min
d. 69 mL/min

Show the answer and explanation

Answer: a. 31 mL/min

CrCl = [(140 - 80) x 55 x 1.23] / 110 = 4,059 / 110 = 36.9 mL/min, and x 0.85 for a female = 31.4, about 31 mL/min. Forgetting the female factor gives 37 mL/min, dividing by 0.85 instead of multiplying gives 43 mL/min, and using weight in pounds (121 lb) gives 69 mL/min. A normal-looking serum creatinine can hide reduced clearance in a small older woman. Source: Cockcroft DW, Gault MH. Nephron 1976;16:31; KDIGO 2024 CKD guideline, ch. 4 (medication management); 2023 AGS Beers Criteria (renal dosing table).

Common mistake

Being reassured by a 'normal' serum creatinine in a small older patient.

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