Question 1

Should I use CKD-EPI or Cockcroft-Gault for drug dosing?

Accepted Answer

It depends on the drug. Most FDA-approved package inserts and Lexicomp/Micromedex renal dosing tables are anchored to creatinine clearance estimated by Cockcroft-Gault. CKD-EPI is preferred for CKD staging and KDIGO classification but was not the basis of most renal-dosing pharmacokinetic studies. Many institutions accept either; if a discrepancy crosses a dosing threshold, the safer course is usually to defer to the package insert convention.

Question 2

Why was the race coefficient removed from CKD-EPI?

Accepted Answer

The original CKD-EPI 2009 and MDRD equations included a Black race multiplier (~1.16) derived from population-level differences in muscle mass / creatinine generation. In 2021 the NKF/ASN task force concluded that race is a social rather than biological category and that retaining the multiplier risked systematic under-recognition of CKD. The race-free 2021 equation (slightly recalibrated) is now the KDIGO-recommended standard.

Question 3

Is eGFR accurate in acute kidney injury?

Accepted Answer

No. All creatinine-based eGFR formulas assume steady-state. In AKI, serum creatinine lags behind real-time GFR by 24–48 hours. None of these equations should be used to estimate current GFR in a patient whose creatinine is rising or falling — including for drug dosing.

Question 4

When should I use cystatin C instead of creatinine?

Accepted Answer

Cystatin C is preferred when serum creatinine is unreliable: severe sarcopenia, cirrhosis, paraplegia, amputation, anorexia, and very elderly patients. The combined CKD-EPI creatinine + cystatin C equation outperforms either marker alone in these situations.

Question 5

What weight should I use for Cockcroft-Gault in obesity?

Accepted Answer

Convention is mixed. The original CG used actual body weight, which overestimates CrCl in obesity. Many references switch to ideal body weight when actual is more than 30% over IBW; some use adjusted body weight. Drug-specific guidance is the most reliable arbiter.

Formula	Value	Units
CKD-EPI 2021race-free	56	mL/min/1.73 m²
MDRD (4-var, no race)	51	mL/min/1.73 m²
Cockcroft-Gault	60	mL/min

eGFR — CKD-EPI 2021, MDRD, Cockcroft-Gault

References

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