Which factors influence eGFR calculation equations like CKD-EPI or MDRD?

• A. Blood glucose and HbA1c
• B. Serum creatinine, age, sex, race, and body size
• C. Urine output and hydration status
• D. Serum potassium

Answer: (B)

eGFR estimation is drawn from serum creatinine and adjustments for differences in how creatinine is produced and handled in the body. Serum creatinine reflects kidney filtration, but its level is also shaped by muscle mass—more muscle means more creatinine production. That’s why age, sex, race, and body size are included: they capture variations in muscle mass and overall body composition so the same creatinine level corresponds to different actual kidney function in different people. Body size, often linked to body surface area, helps normalize the estimate to the person’s size, since larger individuals generally have higher creatinine production. The other factors listed don’t feed into the calculation: blood glucose and HbA1c relate to diabetes control, not filtration rate; urine output and hydration can transiently affect creatinine but aren’t inputs in the standard equation; serum potassium is an electrolyte, not part of these GFR equations.