I recently encountered an otherwise healthy 35 year old woman with a serum creatinine of 2.5 mg/dL (elevated). An initial workup was negative. Further questioning revealed that she was taking creatine supplements to enhance exercise. The supplements were stopped, and a repeat creatinine was 1.0 mg/dL (normal).
Creatine is converted into creatinine, which apparently explained the increased value. I was surprised that creatine supplements could lead to an increase in creatinine of this magnitude. I routinely ask about over the counter medications and supplements, but this experience suggests that patients with otherwise unexplained serum creatinines should be asked specifically about creatine supplementation.
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