Which factors are used in estimating the eGFR?

• A. Serum creatinine with age, sex, and race
• B. Urine protein excretion
• C. Blood urea nitrogen
• D. Serum creatinine only

Answer: (A)

Estimating GFR hinges on how much creatinine is in the blood and how that level should be interpreted given who you are. Creatinine comes from muscle, so people with more muscle mass naturally have higher baseline creatinine production. To translate a given creatinine level into kidney filtration rate, the calculation also adjusts for age, sex, and race because these factors influence expected muscle mass and creatinine generation. The CKD-EPI and MDRD equations combine serum creatinine with age, sex, and race to estimate GFR more accurately than creatinine alone.

Urine protein excretion reflects kidney damage or disease activity, not the rate at which the kidneys filter blood, so it isn’t used to estimate GFR. Blood urea nitrogen relates to kidney function but isn’t a standard input in the current eGFR formulas. Using serum creatinine alone would ignore differences in muscle mass and demographic factors, leading to inaccurate estimates of GFR.