Question 1

What is the difference between the 2009 and 2021 CKD-EPI equations?

Accepted Answer

The 2021 equation removed the race coefficient. For Black patients, the 2021 equation gives a lower eGFR than the 2009 equation at the same creatinine. The 2009 equation may overestimate GFR in Black individuals, potentially delaying CKD diagnosis.

Question 2

Should I use CKD-EPI or Cockcroft-Gault?

Accepted Answer

CKD-EPI is preferred for eGFR reporting and CKD staging. Cockcroft-Gault was historically used for drug dosing but many drug dose recommendations now use CKD-EPI or measured GFR. Check local formularies for which eGFR equation is referenced.

Question 3

What factors interfere with creatinine-based eGFR?

Accepted Answer

Extremes of muscle mass (amputees, bodybuilders, malnutrition), dietary creatine intake, drugs that inhibit tubular creatinine secretion (cimetidine, trimethoprim), and certain assay interferences (ketones, bilirubin). Cystatin C-based eGFR (not included here) may provide complementary information in these cases.

Question 4

Is eGFR accurate in acute kidney injury?

Accepted Answer

No. eGFR equations assume steady-state kidney function. In AKI, creatinine is rising and eGFR will overestimate actual GFR. Use the AKI staging criteria (creatinine rise and urine output) rather than eGFR during acute illness.