Which factor is NOT typically included in CKD-EPI or MDRD eGFR equations?

• A. Body hair color
• B. Serum creatinine
• C. Age
• D. Race

Answer: (A)

Estimating eGFR uses a biomarker tied to kidney filtration—serum creatinine—and adjusts for factors that influence creatinine production. The core inputs are serum creatinine, age, sex, and race. Serum creatinine reflects how well the kidneys are filtering; age and sex adjust for differences in muscle mass and thus creatinine generation; race accounts for population-level differences in baseline creatinine production. Body hair color has no physiological link to kidney function or creatinine production, so it isn’t part of these equations. That’s why hair color is the factor not included. The other options are indeed part of how CKD-EPI and MDRD formulas estimate GFR.