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.
6,709 US adult Third National Health and Nutrition Examination Survey participants.
Absolute percentage of difference in prevalence of stage 3 or 4 CKD between creatinine- and cystatin C-based estimating equations by level of BMI.
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)).
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).
No gold-standard measure of GFR was available.
BMI may influence the estimated prevalence of stage 3 or 4 CKD when cystatin C-based equations are used.