Use a serum creatinine blood test result
Use age
Use sex
Use race only if the lab still uses a race-based equation
Apply a validated equation such as CKD-EPI or MDRD
For CKD-EPI creatinine equation, calculate eGFR from serum creatinine, age, and sex
For more accuracy in some cases, use cystatin C or a combined creatinine-cystatin C equation
For children, use the Schwartz equation
For very unusual body size, muscle mass, pregnancy, or rapidly changing kidney function, consider measured GFR instead of eGFR
Ask the laboratory report for the automatically calculated eGFR if available