GFR Estimation

CKD Managementmedium

A clinician is choosing between the CKD-EPI and MDRD creatinine-based equations to estimate GFR. Which of the following statements comparing these equations is correct?

  1. A.CKD-EPI is more accurate than MDRD when eGFR is above 60 mL/minCorrect
  2. B.MDRD tends to overestimate GFR at higher measured GFR values
  3. C.The two equations differ because MDRD incorporates cystatin C
  4. D.Both equations are validated for use during acute kidney injury

Explanation

The CKD-EPI 2009 creatinine equation was developed to overcome the systematic underestimation of GFR by MDRD at higher levels; CKD-EPI has less bias and greater accuracy, particularly when eGFR is above 60 mL/min/1.73 m². MDRD underestimates (not overestimates) GFR at higher values. Both standard equations use serum creatinine (not cystatin C in these creatinine-based versions), and neither is valid in AKI because they assume a steady state.

Why each option

A.
Correct. CKD-EPI is more accurate and less biased than MDRD, especially at eGFR >60 mL/min/1.73 m².
B.
Incorrect. MDRD systematically underestimates GFR at higher values.
C.
Incorrect. The creatinine-based CKD-EPI and MDRD equations both use creatinine; cystatin C is used in separate equations.
D.
Incorrect. Estimating equations assume steady-state creatinine and are not valid during AKI.

Reference: Levey AS et al. A new equation to estimate glomerular filtration rate (CKD-EPI). Ann Intern Med. 2009;150(9):604-612.

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