Renal function
CreatinineCr
Muscle-derived metabolite cleared by glomerular filtration; the practical GFR surrogate.
Sample
Serum
Clinical reference range
0.7 to 1.3 mg/dL
Adult male
Conv: 0.7–1.3 mg/dLFunc: 0.7–0.9 mg/dL
Biology
What it measures
Creatinine is generated at a relatively steady rate from muscle creatine phosphate and freely filtered. A small amount is secreted by tubules — masking early GFR decline.
Clinical use
Why we order it
Estimate GFR (CKD-EPI 2021), monitor AKI, dose drugs.
Lens · Clinical
Interpretation by lens
Clinical interpretation
Use eGFR, not raw creatinine. AKI: rise ≥0.3 mg/dL in 48 h or ≥1.5× baseline in 7 d (KDIGO).
Research note
The 2021 CKD-EPI equation removed the race coefficient; this substantially reclassifies many Black adults' eGFR upward — clinically relevant for transplant listing.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Reduced GFR (any cause)
- ↑Increased muscle mass / creatine supplementation
- ↑Drugs that block tubular secretion without true GFR change (cimetidine, trimethoprim, cobicistat)
- ↑Cooked meat ingestion (transient)
Causes of LOW
- ↓Low muscle mass (frailty, amputation, paraplegia)
- ↓Pregnancy (increased GFR)
- ↓Severe liver disease
Pitfalls
Pre-analytic & interpretation traps
- !Creatinine is insensitive to early GFR loss — a 'normal' value can mask 50% nephron loss in frail patients.
- !Cystatin C is a useful adjunct when muscle mass is atypical.
Follow-up orders
Logical next-step labs
Related