Creatinine — Normal Range & Interpretation

Clinical Context

Creatinine is a waste product of muscle metabolism that the kidneys filter and excrete. Because production stays relatively constant based on muscle mass, serum creatinine directly reflects glomerular filtration and serves as the primary marker of renal function. Clinicians pair it with BUN and eGFR to stage chronic kidney disease, adjust medication dosing, and detect acute kidney injury before symptoms develop.

Elevated creatinine points to decreased renal perfusion from dehydration, heart failure, or shock; intrinsic kidney damage from nephrotoxic drugs such as NSAIDs, aminoglycosides, and contrast dye; or postrenal obstruction from BPH or stones. Rhabdomyolysis and high-protein intake also raise levels. Decreased creatinine reflects reduced muscle mass, pregnancy, or advanced liver disease. NPs must recognize that elderly and frail patients show falsely reassuring values despite significant renal impairment.

Classic AANP vignette: creatinine in a clinical scenario requiring medication adjustment, particularly metformin, which is contraindicated when eGFR drops below 30. Expect questions linking rising creatinine to ACE inhibitor or ARB initiation, NSAID use in older adults, and contrast-induced nephropathy. The exam emphasizes the creatinine-to-BUN ratio for distinguishing prerenal from intrinsic causes and recognizing that a doubling of creatinine represents roughly a 50 percent loss of kidney function, making trends more valuable than single values.

Related Labs

• Sodium (Na) — mEq/L
• Potassium (K) — mEq/L
• Chloride (Cl) — mEq/L
• CO2 (Bicarbonate) — mEq/L
• BUN — mg/dL

Sources

• MedlinePlus
• ARUP Consult