Original Investigation The CKD Outcomes and Practice Patterns Study (CKDopps): Rationale and Methods Laura Mariani, MD, MS, 1,2 Be ´ne ´ dicte Stengel, MD, PhD, 3 Christian Combe, MD, PhD, 4,5 Ziad A. Massy, MD, PhD, 3,6 Helmut Reichel, MD, 7 Danilo Fliser, MD, 8 Roberto Pecoits-Filho, MD, PhD, 9 Antonio A. Lopes, MD, MPH, PhD, 10 Kunihiro Yamagata, MD, PhD, 11 Takashi Wada, MD, PhD, 12 Michelle M.Y. Wong, MD, MSc, 1 Elodie Speyer, PhD, 1 Friedrich K. Port, MD, MS, 1,2 Ronald L. Pisoni, PhD, MS, 1 and Bruce M. Robinson, MD, MS 1,2 Background: Minimizing clinical complications in patients with advanced chronic kidney disease (CKD) and improving the transition to dialysis therapy and transplantation represents a challenge, requiring reliable evi- dence regarding the effects of CKD care on outcomes. Study Design: The CKD Outcomes and Practice Patterns Study (CKDopps) is a new international pro- spective cohort study designed to describe and evaluate variation in nephrologist-led CKD practices. Setting & Participants: CKDopps is underway in Brazil, France, Germany, Japan, and the United States. Diverse national samples of nephrology clinics are being recruited based on random selection stratified by geographic region and clinic characteristics. CKDopps aims to enroll 12,200 non2dialysis-dependent patients with CKD (75% and 25% with estimated glomerular filtration rates , 30 and 30-,60 mL/min/1.73 m 2 , respectively) to be followed up for 3 to 5 years. Predictors: Demographic, comorbid condition, laboratory, and treatment-related variables are collected at 6-month intervals; patient-reported data are collected annually and more frequently near the transition to end- stage kidney disease; nephrologist practice surveys are collected annually. Outcomes: Outcomes include mortality, end-stage kidney disease, other clinical events (eg, acute kidney injury, hospitalizations, infections, cardiovascular events, and transplant wait-listing), and patient-reported outcomes. Results: For the targeted sample size of 12,200 patients and 160 clinics, CKDopps has 80% power to detect HRs of 1.31 for mortality and 1.19 for mortality or transition to end-stage kidney disease. Limitations: CKDopps does not capture care provided in settings outside nephrology clinics (eg, primary care) or patients with CKD not receiving medical care. Conclusions: CKDopps is designed to characterize nephrology clinic practice variation and identify practices associated with better outcomes, with particular focus on advanced CKD, transition to end-stage kidney disease, and the patient experience. Because data will be collected during routine clinical care in real-world practice, analyses may yield practical readily implementable findings. CKDopps aims to establish a multinational infrastructure for research, collaboration, and ancillary investigation. Additional countries are encouraged to join. Am J Kidney Dis. -(-):---. ª 2016 by the National Kidney Foundation, Inc. INDEX WORDS: Chronic kidney disease (CKD); end-stage kidney disease (ESKD); patient outcomes; dialysis; treatment options; international comparisons; geographic variation; practice patterns; practice variation; transition to ESKD; renal outcome; nephrology care; nephrology clinic; CKDopps. T he burden of chronic kidney disease (CKD) is increasing internationally, consequent to an aging population and increasing prevalence of CKD-associated conditions, including diabetes, hypertension, and obesity. 1-7 Its prevention and management are widely recognized as a public health priority, with variable increases expected interna- tionally in these conditions. 8-14 In the United States, From the 1 Arbor Research Collaborative for Health; 2 Univer- sity of Michigan, Ann Arbor, MI; 3 University Paris-Saclay, University Paris-Sud, UVSQ, CESP, Centre for Research in Epidemiology and Population Health, Inserm UMR1018, F-CRIN- INI-CRCT, Villejuif; 4 Service de Néphrologie Transplantation Dialyse, Centre Hospitalier Universitaire de Bordeaux; 5 Inserm, U1026, Universitaire Bordeaux, Bordeaux; 6 Division of Nephrology, Ambroise Paré University Hospital, APHP, Univer- sity of Paris Ouest-Versailles-St-Quentin-en-Yvelines (UVSQ), Boulogne-Billancourt/Paris, France; 7 Nephrological Center, Vil- lingen-Schwenningen; 8 Internal Medicine IV – Renal and Hy- pertensive Diseases, Saarland University Medical Centre, Homburg/Saar, Germany; 9 School of Medicine, Pontifícia Universidade Católica do Paraná, Curitiba; 10 Faculdade de Medicina da Bahia, Universidade Federal da Bahia, Salvador, BA, Brazil; 11 Department of Nephrology, University of Tsukuba, Tsukuba; and 12 Department of Nephrology and Laboratory Medicine, Kanazawa University, Kanazawa, Japan. Received November 16, 2015. Accepted in revised form March 9, 2016. Address correspondence to Laura Mariani, MD, MS, Arbor Research Collaborative for Health, 340 E Huron St, Ste 300, Ann Arbor, MI 48104. E-mail: laura.mariani@arborresearch.org Ó 2016 by the National Kidney Foundation, Inc. 0272-6386 http://dx.doi.org/10.1053/j.ajkd.2016.03.414 Am J Kidney Dis. 2016;-(-):--- 1