Concordance Between MDR^eGFR, CKDEPI and CockcroftGault Equations in Chronic Kidney Disease

Estimating glomerular filtration rate (eGFR) is central to the diagnosis, staging, and management of chronic kidney disease (CKD). The three most widely used equations are:

• MDRD (Modification of Diet in Renal Disease) Study equation
• CKDEPI (Chronic Kidney Disease Epidemiology Collaboration) equation
• CockcroftGault (CG) equation

Why Concordance Matters

Clinicians often encounter different eGFR values for the same patient depending on the formula applied. Discrepancies can influence:

• CKD staging (e.g., stage3a vs. 3b)
• Drug dosing, especially for renally cleared medications
• Referral decisions to nephrology
• Eligibility for transplant evaluation or clinical trials

Understanding the degree of agreementor lack thereofhelps decide which equation is most appropriate for a given clinical scenario.

Key Differences Among the Equations

Evidence on Concordance

Overall Correlation

Large cohort studies (e.g., NHANES, CKDEPI validation) report Pearson correlation coefficients of 0.850.95 between MDRD and CKDEPI, indicating strong linear agreement. The CG equation shows a slightly lower correlation (r0.80) with the two eGFR formulas, largely because it does not standardize for body surface area.

Bias and Limits of Agreement

BlandAltman analyses consistently reveal a systematic bias:

• MDRD vs. CKDEPI: MDRD tends to be 35mL/min/1.73m lower at eGFR>60mL/min/1.73m.
• CG vs. CKDEPI: CG can be higher or lower by up to 10mL/min depending on weight extremes and age.

These differences are clinically relevant near staging thresholds (e.g., 45, 60mL/min/1.73m).

Subgroup Analyses

Age In patients >75years, CG often overestimates GFR because serum creatinine decreases with sarcopenia, while MDRD and CKDEPI remain closer.

Body Mass Index (BMI) In obesity (BMI>30kg/m), CG using actual weight may overestimate GFR; using adjusted body weight improves agreement with CKDEPI.

Race The race coefficient in MDRD and CKDEPI inflates eGFR for selfidentified Black patients. Recent guidelines suggest removing the coefficient, which reduces the discrepancy between MDRD/CKDEPI and CG in this group.

Clinical Implications

Staging and Referral

When a patients eGFR hovers around a staging cutoff, using CKDEPI is recommended because of its better performance at higher GFR values. If a decision about nephrology referral depends on a specific threshold, report the value from both MDRD and CKDEPI and note any discordance.

Drug Dosing

Many drugdose adjustment guidelines are based on CGderived creatinine clearance (CrCl). For medications with narrow therapeutic windows (e.g., aminoglycosides, vancomycin, direct oral anticoagulants), calculate CG in addition to eGFR and, when possible, verify with measured CrCl.

Research and Registry Data

Registries that span many years often have MDRD as the historic standard. Transitioning to CKDEPI improves longitudinal consistency but requires a conversion algorithm or parallel reporting during the transition period.

Practical Recommendations for the Clinician

1. Firstline estimate: Use CKDEPI for routine reporting of eGFR; it is the most accurate across the full spectrum of kidney function.
2. When weight matters: Calculate CG (preferably with adjusted body weight for BMI>30kg/m) if you need a renalclearance estimate for dosing.
3. Report both values when the estimate is close to a therapeutic or referral threshold.
4. Document the equation and any assumptions (e.g., race coefficient, bodysize adjustments) in the medical record.
5. Consider measured GFR (iothalamate, inulin, or 24h CrCl) when precise assessment is requiredespecially in transplant evaluation or dialysis planning.

Future Directions

Emerging biomarkers (cystatinC, trace protein) and combined equations (creatinine+cystatinC) further reduce bias, especially in extremes of muscle mass. Until these become routine, clinicians should remain aware of the systematic differences among MDRD, CKDEPI and CockcroftGault and choose the formula that aligns with the clinical question.

For a quick bedside tool, many electronic health records now display CKDEPI automatically, with an optional CG calculator accessible under medication dosing modules.

**Key Takeaway:** CKDEPI offers the best overall concordance with the other equations while maintaining accuracy at higher GFRs. CockcroftGault remains indispensable for drug dosing, but it should be interpreted alongside CKDEPI, especially in patients with atypical body habitus or advanced age.

For further reading, see:

• Levey AS etal. A New Equation to Estimate Glomerular Filtration Rate. Ann Intern Med. 2009.
• Inker LA etal. Estimating Glomerular Filtration Rate from Serum Creatinine and Cystatin C. N Engl J Med. 2012.
• Bokenkamp A etal. The CockcroftGault Equation: Still Useful after 45Years? Kidney Int. 2021.