Original Investigation
Pathogenesis and Treatment of Kidney Disease
Accuracy of the MDRD (Modification of Diet in Renal Disease) Study and CKD-EPI (CKD Epidemiology Collaboration) Equations for Estimation of GFR in the Elderly

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Background

Glomerular filtration rate (GFR) is a measure of kidney function, commonly estimated using equations that adjust serum creatinine concentration for age, race, and sex. The Modification of Diet in Renal Disease (MDRD) Study equation is widely used, but underestimates GFR at higher levels. The serum creatinine–based Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPIcr) equation generally provides more accurate estimation at GFR >60 mL/min/1.73 m2. Newer equations have been reported using cystatin C concentration either alone (CKD-EPIcys) or in combination with creatinine concentration (CKD-EPIcr-cys). None of these equations has been well validated in older people. We tested the accuracy of these equations in people 74 years or older compared with GFR measured by a reference method.

Study Design

Diagnostic test evaluation in a prospective cohort.

Setting & Participants

Participants (n = 394; median age, 80 [range, 74-97] years) recruited from nephrology clinics and the community.

Index Test

GFR estimated using the MDRD Study, CKD-EPIcr, CKD-EPIcys and CKD-EPIcr-cys equations.

Reference Test

GFR measured using an iohexol clearance method.

Results

Median measured GFR was 53.4 (range, 7.2-100.9) mL/min/1.73 m2. MDRD Study–, CKD-EPIcr–, and CKD-EPIcr-cys–estimated GFRs overestimated GFR (median differences of 3.5 [P< 0.001], 1.7 [P < 0.001], and 0.8 [P = 0.02] mL/min/1.73 m2, respectively); the CKD-EPIcys equation was unbiased. Accuracy (percentage of estimates within 30% of measured GFR [P30]) was 81%, 83%, 86%, and 86% for the MDRD Study, CKD-EPIcr, CKD-EPIcys, and CKD-EPIcr-cys equations, respectively. Accuracy of the MDRD Study equation was inferior (P = 0.004) to the CKD-EPIcr equation at GFR >60 mL/min/1.73 m2.

Limitations

Those of non-European ancestry were not included. For practical reasons, only a 4-hour sampling protocol was used for iohexol clearance.

Conclusions

The CKD-EPIcr equation appeared less biased and was more accurate than the MDRD Study equation. No equation achieved an ideal P30 in the overall population. Our data suggest that GFR estimation is as satisfactory in older people of European ancestry as it has been reported to be in younger individuals.

Section snippets

Participant Selection

Participants were either patients known to the Kent Kidney Care Centre or residents of the local population. The latter were recruited through a variety of means, including the researchers attending discussion groups in Age Concern centers, golf clubs, Rotary clubs, and residential care homes, and through advertising the study by media briefings in hospital newsletters, local newspapers, and radio stations. Overall, 38% of participants were recruited through nephrology clinics, and 62%, through

Results

A total of 398 individuals were recruited to the study. An additional 27 individuals initially agreed to participate but subsequently withdrew, for reasons including intercurrent illness at the time of the scheduled test, refusal for participation from family members, and inability to provide alternative arrangements for their dependents. Three individuals of African-Caribbean ethnicity and one amputee were excluded from the final analyses on the basis that as subgroups, they were too small to

Discussion

We present a large prospective evaluation of the performance of contemporary GFR estimating equations in older people. Overall, our data suggest that these equations perform as well in the older population as in younger people and that there may be marginal benefits in using one of the CKD-EPI equations compared to the MDRD Study equation.

Several studies have been undertaken directly comparing the MDRD Study and CKD-EPIcr equations: a variety of statistical approaches have been used. In this

Acknowledgements

We thank the staff of Clinical Biochemistry and The Kent Kidney Care Centre, East Kent Hospitals University NHS (National Health Service) Foundation Trust for their cooperation and help. The study received statistical advice at the proposal stage from Drs A. Laurence and E. Bassett of the Institute of Mathematics, Statistics and Actuarial Science, University of Kent, Canterbury, Kent. Mr Paul Bassett, Statsconsultancy Ltd, Amersham, Buckinghamshire, UK, helped with data analysis.

Support: The

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    Originally published online August 13, 2012.

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