Serum creatinine depends on muscle mass as well as kidney function. In cirrhosis, malnutrition, frailty and prolonged critical illness, creatinine production falls, so a 'normal' creatinine can hide significantly reduced clearance. Bilirubin can also interfere with some creatinine assays.
Equations built on creatinine, including Cockcroft-Gault and eGFR, inherit this error. For renally cleared drugs with narrow margins — vancomycin, aminoglycosides, some antivirals and low-molecular-weight heparins — use drug levels where available, and consider cystatin C where renal function matters for dosing.
- Treat a normal creatinine with caution in cirrhosis, frailty, malnutrition or long ICU stays.
- Use drug levels to guide narrow-margin renally cleared drugs in these patients.
- Consider cystatin C when an accurate estimate of renal function changes dosing.
- Recheck renal function and levels as the clinical picture changes.
Why it matters
It is the most common reason renally cleared drugs accumulate in patients whose kidney function 'looked normal'.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for clinical pharmacology, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free