Diagnostic Pitfalls, Creatine Supplementation, Physical Activity, and Kidney Function Assessment in Non-Dialysis Chronic Kidney Disease: A Narrative Review

Abstract

Creatine supplementation is widely used by physically active people. In patients with non dialysis chronic kidney disease, it may complicate laboratory assessment of kidney function because serum creatinine reflects both glomerular filtration and creatinine generation. Creatine intake, muscle mass, diet, and physical activity may influence serum creatinine independently of true glomerular filtration rate. This narrative review discusses interpretation of kidney function markers in patients with non dialysis chronic kidney disease who use creatine supplementation, especially in the context of physical activity or resistance training. Creatine may increase serum creatinine without a parallel reduction in true glomerular filtration rate. Creatinine based equations may translate a non filtration related creatinine rise into a lower estimated glomerular filtration rate. Physical activity may add complexity because intense exercise, muscle injury, dehydration, or exertional rhabdomyolysis may also affect creatinine, creatine kinase, and kidney function markers. Supplement history and recent training load should be interpreted together with cystatin C, albuminuria, urinary sediment, biochemical abnormalities, and clinical status. Increased serum creatinine should be treated as a diagnostic ambiguity rather than automatically classified as kidney deterioration or benign artefact. Worsening cystatin C based estimated glomerular filtration rate, increasing albuminuria, active urinary sediment, biochemical abnormalities, oliguria, edema, hypertension, or signs of exercise related muscle injury should prompt evaluation for true kidney function deterioration.