Research Article Variability in Estimated Glomerular Filtration Rate by Area under the Curve Predicts Renal Outcomes in Chronic Kidney Disease Szu-Chia Chen, 1,2,3 Ming-Yen Lin, 1 Teng-Hui Huang, 4 Chi-Chih Hung, 1,3 Yi-Wen Chiu, 1,5 Jer-Ming Chang, 1,2,3 Jer-Chia Tsai, 1,5 Shang-Jyh Hwang, 1,5 and Hung-Chun Chen 1,5 1 Division of Nephrology, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan 2 Department of Internal Medicine, Kaohsiung Municipal Hsiao-Kang Hospital, Kaohsiung Medical University, Kaohsiung 807, Taiwan 3 Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan 4 Department of Public Health, Kaohsiung Medical University, Kaohsiung 807, Taiwan 5 Faculty of Renal Care, College of Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan Correspondence should be addressed to Jer-Chia Tsai; jerchia@kmu.edu.tw Received 16 July 2014; Revised 9 September 2014; Accepted 9 September 2014; Published 23 October 2014 Academic Editor: Allen R. Nissenson Copyright © 2014 Szu-Chia Chen et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Greater variability in renal function is associated with mortality in patients with chronic kidney disease (CKD). However, few studies have demonstrated the predictive value of renal function variability in relation to renal outcomes. Tis study investigates the predictive ability of diferent methods of determining estimated glomerular fltration rate (eGFR) variability for progression to renal replacement therapy (RRT) in CKD patients. Tis was a prospective observational study, which enrolled 1,862 CKD patients. Te renal end point was defned as commencement of RRT. Te variability in eGFR was measured by the area under the eGFR curve (AUC)%. A signifcant improvement in model prediction was based on the −2 log likelihood ratio statistic. During a median 28.7-month follow-up, there were 564 (30.3%) patients receiving RRT. In an adjusted Cox model, a smaller initial eGFR AUC% 12M ( < 0.001), a smaller peak eGFR AUC% 12M ( < 0.001), and a larger negative eGFR slope 12M ( < 0.001) were associated with a higher risk of renal end point. Two calculated formulas: initial eGFR AUC% 12M and eGFR slope 12M were the best predictors. Our results demonstrate that the greater eGFR variability by AUC% is associated with the higher risk of progression to RRT. 1. Introduction Chronic kidney disease (CKD) is an increasing worldwide public health problem associated with increased morbidity and mortality [1, 2]. Greater variability in renal function is associated with high mortality in CKD [3]. Te mechanisms of variability in renal function are multifactorial, including intrinsic renal disease (e.g., renal microvascular disease or impaired autoregulatory mechanisms) and extrinsic factors (e.g., volume status and presence and severity of concurrent illness). However, only limited studies have demonstrated the predictive value of renal function variability in relation to renal outcomes in CKD patients. Plotting slopes of 1/creatinine or estimated glomerular fltration rate (eGFR) versus time has been used as a tool for outcome variable in clinical studies [4]. eGFR slope has been identifed as an independent risk factor for cardiovascular morbidity and mortality and progression to end-stage renal disease [5–10]. It is necessary to obtain the summarized infor- mation in the multivariate data by repeated measurement. Dynamic fuctuations in eGFR slope change may contribute to additional prognostic information beyond cross-sectional data. Te area under the curve (AUC) computed with the trapezoidal formula is widely used as an approach to measure the dynamic and accumulating change of clinical laboratory parameters [11–14], but little is known about its application in the repeated measurements of eGFR variability. Te eGFR AUC% formula by repeated measurements of eGFR was used as a measure of variability in renal function in our study. We Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 802037, 8 pages http://dx.doi.org/10.1155/2014/802037