CKD-EPI vs MDRD — eGFR Equations

CKD Managementmedium

A 45-year-old healthy man with serum creatinine 1.2 mg/dL (no CKD risk factors, no proteinuria) undergoes a routine health check. His eGFR calculated by the MDRD equation is 61 mL/min/1.73m² (GFR category G2), but by the 2021 CKD-EPI equation it is 74 mL/min/1.73m² (normal). Which of the following best explains this discrepancy and the preferred approach?

  1. A.MDRD is more accurate than CKD-EPI across all GFR ranges
  2. B.CKD-EPI (2021) is preferred; MDRD underestimates GFR >60 and over-diagnoses CKDCorrect
  3. C.The gap reflects a race coefficient; use race-adjusted MDRD
  4. D.Neither creatinine equation is valid >60; a 24-h creatinine clearance is required

Explanation

The MDRD (Modification of Diet in Renal Disease) equation was developed and validated in CKD patients with low GFR, it systematically underestimates GFR at higher values (>60 mL/min/1.73m²), leading to over-classification of patients as having CKD. The 2009 CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation and its 2021 revision (CKD-EPI 2021, which REMOVED the race coefficient after recognition that race is a social construct without biological basis for kidney function) are more accurate across the full range of GFR, particularly at GFR >60. The 2021 CKD-EPI is the current KDIGO-recommended equation for eGFR reporting in adults. For patients at extremes (muscle-wasting diseases, amputees, very high or low muscle mass), cystatin C-based eGFR or combined creatinine+cystatin C equations (CKD-EPI cys 2021) improve accuracy. Note: an eGFR of 60–89 is GFR category G2 but does not by itself constitute CKD, which also requires a marker of kidney damage (e.g., albuminuria or a structural abnormality) present for >3 months; this healthy man with no proteinuria does not have CKD.

Why each option

A.
Incorrect. MDRD is less accurate at higher GFR (>60), where it is biased and underestimates; CKD-EPI is preferred there.
B.
Correct. MDRD was derived in low-GFR CKD populations and underestimates GFR >60, over-classifying healthy people as CKD. The 2021 (race-free) CKD-EPI creatinine equation is KDIGO-preferred; a cystatin C–based estimate can confirm a borderline value.
C.
Incorrect. The 2021 CKD-EPI equations removed the race coefficient; the discrepancy is MDRD’s high-GFR bias, not race adjustment.
D.
Incorrect. A 24-hour creatinine clearance is not required; cystatin C–based eGFR is the preferred confirmatory test for a borderline value.

Reference: Inker LA, NEJM 2021 (CKD-EPI 2021); Levey AS, Ann Intern Med 2009; KDIGO CKD 2024

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