Measure serum creatinine
Use age, sex, and sometimes race or body size
Calculate estimated glomerular filtration rate (eGFR)
Common eGFR equations: CKD-EPI, MDRD, Cockcroft-Gault
For Cockcroft-Gault: creatinine clearance = [(140 – age) × weight in kg] / (72 × serum creatinine)
Multiply Cockcroft-Gault result by 0.85 for females
Assess urine albumin-to-creatinine ratio
Check serum urea/BUN if needed
Consider measured creatinine clearance from 24-hour urine collection
Consider cystatin C-based eGFR if creatinine is unreliable
Interpret results with clinical context and trend over time