Original Investigation
Pathogenesis and Treatment of Kidney Disease
Comparison of the Prevalence and Mortality Risk of CKD in Australia Using the CKD Epidemiology Collaboration (CKD-EPI) and Modification of Diet in Renal Disease (MDRD) Study GFR Estimating Equations: The AusDiab (Australian Diabetes, Obesity and Lifestyle) Study

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Background

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) is more accurate than the Modification of Diet in Renal Disease (MDRD) Study equation. We applied both equations in a cohort representative of the Australian adult population.

Study Design

Population-based cohort study.

Setting & Participants

11,247 randomly selected noninstitutionalized Australians aged ≥ 25 years who attended a physical examination during the baseline AusDiab (Australian Diabetes, Obesity and Lifestyle) Study survey.

Predictors & Outcomes

Glomerular filtration rate (GFR) was estimated using the MDRD Study and CKD-EPI equations. Kidney damage was defined as urine albumin-creatinine ratio ≥ 2.5 mg/mmol in men and ≥ 3.5 mg/mmol in women or urine protein-creatinine ratio ≥ 0.20 mg/mg. Chronic kidney disease (CKD) was defined as estimated GFR (eGFR) ≥ 60 mL/min/1.73 m2 or kidney damage. Participants were classified into 3 mutually exclusive subgroups: CKD according to both equations; CKD according to the MDRD Study equation, but no CKD according to the CKD-EPI equation; and no CKD according to both equations. All-cause mortality was examined in subgroups with and without CKD.

Measurements

Serum creatinine and urinary albumin, protein, and creatinine measured on a random spot morning urine sample.

Results

266 participants identified as having CKD according to the MDRD Study equation were reclassified to no CKD according to the CKD-EPI equation (estimated prevalence, 1.9%; 95% CI, 1.4-2.6). All had an eGFR ≥ 45 mL/min/1.73 m2 using the MDRD Study equation. Reclassified individuals were predominantly women with a favorable cardiovascular risk profile. The proportion of reclassified individuals with a Framingham-predicted 10-year cardiovascular risk ≥ 30% was 7.2% compared with 7.9% of the group with no CKD according to both equations and 45.3% of individuals retained in stage 3a using both equations. There was no evidence of increased all-cause mortality in the reclassified group (age- and sex-adjusted hazard ratio vs no CKD, 1.01; 95% CI, 0.62-1.97). Using the MDRD Study equation, the prevalence of CKD in the Australian population aged ≥ 25 years was 13.4% (95% CI, 11.1-16.1). Using the CKD-EPI equation, the prevalence was 11.5% (95% CI, 9.42-14.1).

Limitations

Single measurements of serum creatinine and urinary markers.

Conclusions

The lower estimated prevalence of CKD using the CKD-EPI equation is caused by reclassification of low-risk individuals.

Section snippets

Participants

AusDiab is a population-based survey of adults aged ≥ 25 years. The present report uses cross-sectional data collected at baseline (1999/2000). Details of survey methods and sample selection have been described previously in detail.20 In brief, a representative sample of the population was obtained using a stratified cluster sampling method. Of 17,130 households eligible for inclusion, 11,579 agreed to be interviewed and 20,386 adults completed the household interview. A total of 11,247

Results

Of 11,247 individuals who presented for physical examination at baseline, complete data for kidney function (serum creatinine level, urine albumin-creatinine ratio, and urine protein-creatinine ratio) were available for 99.4% (n = 11,182). Participants were predominantly white (92.9%), with a minority of Asian (5.70%) and indigenous (0.80%) participants. Mean age of participants was 51.5 ± 14.5 (standard deviation [SD]) years and 55.2% were women. Table 1 lists the distribution of CKD stages in

Discussion

The MDRD Study equation has gained widespread acceptance in research and clinical practice in recent years and has been validated in diverse populations.18 Developed based on 1,628 patients with existing CKD, the MDRD Study equation provides accurate estimates across a wide range of subgroups for GFR < 60 mL/min/1.73 m2. However, a well-recognized limitation of this equation is the systematic underestimation of GFR when measured GFR is near or > 60 mL/min/1.73 m2. The CKD-EPI equation,

Acknowledgements

The AusDiab Kidney Study is a substudy of the AusDiab Study.

Support: In addition to support from the AusDiab co-coordinating team led by Professor Paul Zimmet and Associate Professor Jonathan Shaw at the Baker IDI Heart and Diabetes Institute, Melbourne, Australia, their sponsors, and the National Health and Medical Research Council of Australia (NHMRC grant 233200), the AusDiab Kidney Study specifically acknowledges the support of Amgen Australia, Kidney Health Australia, and The Royal Prince

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    Originally published online as doi:10.1053/j.ajkd.2009.12.011 on February 8, 2010.

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