Measure serum creatinine
Calculate estimated glomerular filtration rate (eGFR) using age, sex, and creatinine
Use the CKD-EPI equation for eGFR
Use the MDRD equation if CKD-EPI is unavailable
Calculate creatinine clearance using the Cockcroft-Gault formula
Adjust creatinine clearance for body weight when needed
Measure blood urea nitrogen (BUN)
Check urine albumin-to-creatinine ratio (ACR)
Check urine protein levels
Assess serum cystatin C if available
Compare results with normal reference ranges
Repeat testing over time to assess trend
Use imaging or nuclear medicine tests if a direct GFR measurement is needed