eGFR — CKD-EPI 2021, MDRD, Cockcroft-Gault
Three estimates of kidney function side by side, with CKD staging and a note on which to use for drug dosing.
- Staging CKD or trending kidney function over time
- Renal dosing of a medication where the package insert specifies "CrCl" rather than "eGFR"
- Reconciling a discrepancy between the lab-reported eGFR and your drug-dosing reference
- An older or sarcopenic patient where you suspect creatinine-based estimates are misleading
- The lab's reported eGFR is almost always CKD-EPI 2021 in modern US labs. If you see an MDRD-style number, it's outdated.
- Drug package inserts use Cockcroft-Gault. This is the most common source of confusion between "eGFR is 60, why are we dose-reducing?" — because CG, not eGFR, is what the dosing reference is anchored to.
- All formulas fail in AKI. A serum creatinine that is rising or falling is not at steady state, so no equation gives you a true current GFR.
- Low muscle mass overestimates GFR. Cirrhosis, malnutrition, paraplegia, amputation — these patients can have a "normal" creatinine and a true GFR of 30. Cystatin C is the way to disambiguate.
The three formulas can disagree by 20–30%, and this disagreement is usually invisible because the EHR shows one number. Showing all three side by side surfaces the disagreement and makes drug dosing — which is the most common reason a clinician needs an eGFR — explicit rather than implicit.
| 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 |
CKD stage: G3a (mild–moderate decrease)
- CKD-EPI 2021 is the current KDIGO recommendation and the eGFR most labs report.
- Cockcroft-Gault is creatinine clearance, not GFR, and is what most drug package inserts (and renal dosing tables) anchor to.
- MDRD is the legacy formula — still seen in older studies and some labs.
Frequently asked
Should I use CKD-EPI or Cockcroft-Gault for drug dosing?
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.
Why was the race coefficient removed from CKD-EPI?
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.
Is eGFR accurate in acute kidney injury?
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.
When should I use cystatin C instead of creatinine?
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.
What weight should I use for Cockcroft-Gault in obesity?
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.