Creatinine
Bladder and kidney healthCreatinine is a waste product from muscle metabolism that's filtered by the kidneys and excreted in urine.
Serum levels remain relatively constant with normal kidney function, making it a reliable marker for kidney filtration capacity. Elevated levels suggest reduced kidney function.
Why this matters
Since creatinine production is relatively constant (based on muscle mass), rising blood levels signal declining kidney function. Elevated creatinine often occurs without symptoms until kidney function is significantly impaired. Early detection allows interventions to protect remaining kidney function through blood pressure control, diabetes management, and avoiding kidney-damaging medications.
How this connects to other biomarkers
- Creatinine is the workhorse marker of kidney function but is influenced by muscle mass — always interpret it with estimated Glomerular Filtration Rate (eGFR), and use estimated Glomerular Filtration Rate (eGFR) - Cystatin C in patients with very high or very low muscle mass.
- Elevated Creatinine with elevated Urea and a BUN/Creatinine Ratio > 20 suggests dehydration or upstream causes (volume depletion, GI bleed); a ratio < 10 suggests the kidney itself is damaged.
- Rising Creatinine with elevated Total Creatine Kinase (CK) / Myoglobin indicates kidney injury caused by severe muscle breakdown (rhabdomyolysis).
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