Differential Estimation of CKD Using Creatinine- Versus Cystatin C–Based Estimating Equations by Category of Body Mass Index

Received 20 August 2008; accepted 30 December 2008. published online 27 April 2009.

Backgound

Adiposity is associated with cystatin C. Cystatin C–based glomerular filtration rate (GFR) equations may result in overestimation of chronic kidney disease (CKD) prevalence at greater body mass index (BMI) levels.

Study Design

Cross-sectional.

Setting & Participants

6,709 US adult Third National Health and Nutrition Examination Survey participants.

Factor

BMI.

Outcome

Absolute percentage of difference in prevalence of stage 3 or 4 CKD between creatinine- and cystatin C–based estimating equations by level of BMI.

Measurements

Normal weight, overweight, and obesity were defined as BMI of 18.5 to less than 25.0, 25 to less than 30.0, and 30 kg/m2 or greater, respectively. Stage 3 or 4 CKD (estimated glomerular filtration rate [eGFR], 15 to 59 mL/min/1.73 m2) was defined using the 4-variable creatinine-based Modification of Diet in Renal Disease Study equation (eGFRMDRD); cystatin C level, age, sex, and race equation (eGFRCysC,age,sex,race); cystatin C–only equation (eGFRCysC); cystatin C level of 1.12 mg/L or greater (increased cystatin C); and an equation incorporating serum creatinine level, cystatin C level, age, sex, and race (eGFRCr,CysC,age,sex,race).

Results

Differences in stage 3 or 4 CKD prevalence estimates between eGFRCysC,age,sex,race, eGFRCysC, and increased cystatin C, separately, and eGFRMDRD were greater at higher BMI levels. Specifically, compared with estimates derived using eGFRMDRD for normal-weight, overweight, and obese participants, estimated prevalences of stage 3 or 4 CKD were 2.1%, 3.0%, and 6.5% greater when estimated by using eGFRCysC,age,sex,race (P trend = 0.005); 0.1%, 0.6%, and 2.2% greater for eGFRCysC (P trend = 0.03); 2.9%, 5.2%, and 9.5% greater for increased cystatin C (P trend < 0.001); and −0.1%, −0.4%, and 0.0% greater for eGFRCr,CysC,age,sex,race, respectively (P trend = 0.7).

Limitations

No gold-standard measure of GFR was available.

Conclusions

BMI may influence the estimated prevalence of stage 3 or 4 CKD when cystatin C–based equations are used.

Index Words: Chronic kidney insufficiency, cystatin C, creatinine, glomerular filtration rate, body mass index

1 Center for Health Research, Kaiser Permanente Georgia, Atlanta, GA

2 Framingham Heart Study, National Heart, Lung, and Blood Institute, Framingham, MA

3 Department of Endocrinology and Metabolism, Brigham and Women's Hospital and Harvard Medical School, Boston, MA

4 Department of Epidemiology, Johns Hopkins School of Public Health, Bethesda, MD

5 Department of Medicine, Mount Sinai School of Medicine, New York, NY

6 Department of Community and Preventive Medicine, Mount Sinai School of Medicine, New York, NY

Address correspondence to Suma Vupputuri, PhD, Research Investigator, The Center for Health Research, Kaiser Permanente Georgia, 3495 Piedmont Rd, Bdg 10, Ste 205, Atlanta, GA 30305

Originally published online as doi:10.1053/j.ajkd.2008.12.043 on April 27, 2009.

Because the Editor-in-Chief recused himself from consideration of this manuscript, the Deputy Editor (Daniel E. Weiner, MD, MS, Tufts Medical Center) served as Acting Editor-in-Chief. Details of the journal's procedures for potential editor conflicts are given in the Editorial Policies section of the AJKD website.

PII: S0272-6386(09)00426-0

doi:10.1053/j.ajkd.2008.12.043

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