In the MDRD equation for estimating GFR, which factor is not typically included?

In the MDRD equation for estimating GFR, which factor is not typically included?

• A. Time of day of blood collection
• B. Identification of ethnicity
• C. Body mass
• D. Age

Answer: (A)

The factor tested here is about what the MDRD equation uses to estimate GFR. The MDRD formula estimates GFR from serum creatinine together with a few demographic factors, specifically age, sex, and ethnicity. Time of day when the blood is drawn is not part of the calculation. Why the correct item fits: The equation is built on the idea that kidney function, reflected by creatinine levels, can be adjusted for how old a person is and for differences in muscle mass and biology between sexes and racial groups. That’s why age, sex, and ethnicity appear in the formula. Time of day isn’t incorporated because the original MDRD model relies on a steady-state creatinine value, and diurnal variation isn’t used to modify the estimate. A bit of context: Body mass isn’t a variable in the MDRD equation either—the model uses creatinine, age, sex, and race to account for body size indirectly, which is why body mass isn’t included as a separate factor. The ethnicity factor is typically a multiplier (e.g., adjustments for Black individuals) to reflect observed differences in creatinine generation and GFR.

The factor tested here is about what the MDRD equation uses to estimate GFR. The MDRD formula estimates GFR from serum creatinine together with a few demographic factors, specifically age, sex, and ethnicity. Time of day when the blood is drawn is not part of the calculation.

Why the correct item fits: The equation is built on the idea that kidney function, reflected by creatinine levels, can be adjusted for how old a person is and for differences in muscle mass and biology between sexes and racial groups. That’s why age, sex, and ethnicity appear in the formula. Time of day isn’t incorporated because the original MDRD model relies on a steady-state creatinine value, and diurnal variation isn’t used to modify the estimate.

A bit of context: Body mass isn’t a variable in the MDRD equation either—the model uses creatinine, age, sex, and race to account for body size indirectly, which is why body mass isn’t included as a separate factor. The ethnicity factor is typically a multiplier (e.g., adjustments for Black individuals) to reflect observed differences in creatinine generation and GFR.