Differential estimation of CKD using creatinine- versus cystatin C-based estimating equations by category of body mass index.
BACKGROUND
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.


METHODS
Cross-sectional.


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


METHODS
BMI.


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


METHODS
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/m(2) or greater, respectively. Stage 3 or 4 CKD (estimated glomerular filtration rate [eGFR], 15 to 59 mL/min/1.73 m(2)) was defined using the 4-variable creatinine-based Modification of Diet in Renal Disease Study equation (eGFR(MDRD)); cystatin C level, age, sex, and race equation (eGFR(CysC,age,sex,race)); cystatin C-only equation (eGFR(CysC)); 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 (eGFR(Cr,CysC,age,sex,race)).


RESULTS
Differences in stage 3 or 4 CKD prevalence estimates between eGFR(CysC,age,sex,race), eGFR(CysC), and increased cystatin C, separately, and eGFR(MDRD) were greater at higher BMI levels. Specifically, compared with estimates derived using eGFR(MDRD) 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 eGFR(CysC,age,sex,race) (P trend = 0.005); 0.1%, 0.6%, and 2.2% greater for eGFR(CysC) (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 eGFR(Cr,CysC,age,sex,race), respectively (P trend = 0.7).


CONCLUSIONS
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.
Vupputuri
Suma
S
Center for Health Research, Kaiser Permanente Georgia, Atlanta, GA 30305, USA. suma.vupputuri@kp.org
Fox
Caroline S
CS
Coresh
Josef
J
Woodward
Mark
M
Muntner
Paul
P
D000293:Adolescent; D000328:Adult; D000368:Aged; D015992:Body Mass Index; D002648:Child; D003404:Creatinine / Q000097:blood*; D003430:Cross-Sectional Studies; D055316:Cystatin C / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology; D006801:Humans; D007674:Kidney Diseases / Q000097:blood* / Q000453:epidemiology / Q000503:physiopathology*; D007677:Kidney Function Tests / Q000379:methods / Q000706:statistics & numerical data; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D015995:Prevalence; D055815:Young Adult
D055316:Cystatin C; D003404:Creatinine