Introduction. Cystatin C (CysC) is a glomerular filtration rate (GFR) marker affected by GFR and obesity. Because percentage body fat (%BF) distribution is affected by ethnicity, different measures of %BF may improve CysC prediction. This study aims to create multivariate models that predict serum CysC and determine which %BF metric gives the best prediction. Methods. Serum CysC was measured by nephelometric assay. We estimated %BF by considering weight, body mass index, waist-hip ratio, triceps skin fold, bioimpedance, and Deurenberg and Yap %BF equations. A base multivariate model for CysC was created with a %BF metric added in turn. The best model is considered by comparing values, , Akaike information criterion (AIC), and Bayesian information criterion (BIC). Results. There were 335 participants. Mean serum CysC and creatinine were 1.27？mg/L and 1.44？mg/dL, respectively. Variables for the base model were age, gender, ethnicity, creatinine, serum urea, c-reactive protein, log GFR, and serum albumin. %BF had a positive correlation with CysC. The best model for predicting CysC included bioimpedance-derived %BF (), with the highest (0.917) and the lowest AIC and BIC (？371, ？323). Conclusion. Obesity is associated with CysC, and the best predictive model for CysC includes bioimpedance-derived %BF. 1. Introduction Cystatin C is an endogenous 13？kDa cysteine protease inhibitor filtered by the glomeruli and reabsorbed and catabolized by renal tubular cells. It is considered as an alternative marker of kidney function (glomerular filtration rate, GFR). It is thought to be superior to creatinine as a marker of kidney function because it is less affected by muscle mass and does not seem to be affected by age or gender [1–3]. However, it has been recognized that non-GFR factors also influence serum cystatin C levels. Stevens et al. examined this in chronic kidney disease (CKD) patients and found that, after adjusting for age, gender, sex, and GFR, serum cystatin C was significantly influenced by proteinuria, diabetes status, systolic blood pressure, weight, body mass index (BMI), white blood cell count, hemoglobin, and c-reactive protein [4]. Obesity has been shown to be associated with serum cystatin C levels in several studies [5, 6]. These studies indirectly used several metrics of obesity for analyzing the effects of body fat mass on serum cystatin C levels. Because percentage body fat (%BF) distribution may also be affected by ethnicity, different measures (or estimations) of %BF may improve the prediction of serum cystatin C levels [7, 8]. We hypothesize
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