Creatinine-based eGFR assumes average creatinine generation. It overestimates kidney function in people with low muscle mass, such as those who are frail, malnourished or amputees, and underestimates it in those with high muscle mass or high creatine intake. Creatinine can also be affected by drugs that block tubular secretion, such as trimethoprim.
When a treatment decision depends on the eGFR, for example drug dosing close to a threshold, staging unexpected CKD or assessing a potential donor, check cystatin C or use a measured GFR, rather than relying on one creatinine value. Interpret the result alongside albuminuria and the clinical picture.
- Remember that low muscle mass makes creatinine-based eGFR look better than it is.
- Check cystatin C when the eGFR does not fit the clinical picture or a decision depends on it.
- Consider drugs that raise creatinine without changing true GFR, such as trimethoprim.
- Interpret eGFR together with albuminuria.
Why it matters
Acting on a falsely reassuring eGFR delays CKD diagnosis and can lead to overdosing of renally cleared drugs.
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