To screen or not to screen: that is not (yet) the question.

Resolving the question of whether screening for CKD is effective in improving outcomes for affected individuals is one of the most important questions facing the field of nephrology today. Themedical community has been bombarded by conflicting statements on screening for CKD published by the American Society of Nephrology, the National Kidney Foundation, and the American College of Physicians, which has led to confusion. An eloquent statement from the US Preventive Services Task Force stated the obvious: No recommendation can be made due to lack of evidence (1). Our immediate decision is not whether we will systematically screen for CKD in the United States, but whether we are serious about gathering the evidence needed to make an informed choice. Such effort will require a committed investment of material and intellectual resources and, most of all, patience and perseverance. Early detection and prevention are the cornerstones of public health efforts to reduce the burdenof common chronic diseases. The nephrology community can derive energy and hope from revisiting the history of the great leaps we have achieved in the reduction of cardiovascular morbidity and mortality in the United States by treating high BP. Although the Framingham cohort identified BP as a “factor of risk” in 1961 (2), many of the seminal randomized controlled trials showing the benefit of lowering diastolic, then systolic BP, were not completed until 2–3 decades later. Screening for elevated BP and instituting appropriate treatment remains a national priority today. In nephrology, we are just beginning this journey. CKDwasfirst definedbyconsensus in theKidneyDisease OutcomesQuality Initiative guidelines published in 2002. At that time, CKDwas defined solely on the basis of eGFR. Since then, both eGFR andurine albumin/creatinine ratio (UACR) are required for staging of disease (3). The last decade has been rich in increasing understanding of the epidemiology of CKD (4,5), including the high cardiovascular risk inpersonswithCKD(6) and the identificationof high-risk groups such as racial/ethnicminorities and persons with low socioeconomic status (SES) (7). Despite these advances, observational studies have not convincingly shown that screening for CKD using either eGFR or UACR improves health outcomes or is cost-effective (8– 10). To date, no randomized controlled trial has evaluated the effectiveness of screening for CKD. We believe that “preventive nephrology” should be prioritized by the nephrology community. To move forward, we must gather the evidence to make an informed decision about potential benefits and risks of a systematic CKD screening strategy. In particular, we must (1) identify the populations at highest risk who are most likely to benefit, (2) identify a testing strategy that maximizes sensitivity and specificity and is costeffective, (3) agree on appropriate clinical and patientcentered outcomes relevant to CKD, (4) investigate step-wise algorithms for early, individualized management, and (5) understand risks, costs, and benefits of community-based versus office-based screening, among other steps. In this issue of CJASN, Vart and colleagues move the field further by addressing some of these important questions (11). In this article, the authors aim to identify a CKD screening approach that may enhance the detection of individuals at high risk for cardiovascular complications. Using data from a subset of individuals enrolled in the Prevention of Renal and Vascular End-Stage Disease (PREVEND) study, the authors examinewhether screening for CKD among individuals with low SES or elderly patients in addition to persons with diabetes, hypertension, and cardiovascular disease (traditionally considered high risk) may increase the yield of CKD detection compared with screening for CKD among traditional high-risk individuals alone. In so doing, the authors address the following important questions regarding CKD screening. Which populations would benefit the most from CKD screening? Screening for chronic diseases has the greatest benefit when utilized among communities at highest risk. In the article by Vart et al. (11), the number needed to screen to identify one CKD case was 6.5 in each expanded strategy compared with 5.6 using the traditional strategy. However, the expanded screening strategy including individuals of low SES was able to detect persons with CKD associated with a higher risk for cardiovascular disease compared with persons with no CKD and those with undetected CKD. These data are consistentwith prior studies that demonstrated a high burden of CKD, ESRD, cardiovascular disease, and mortality among low-incomepopulations (12,13). Screening forCKD in disadvantaged communities at high risk was used among Aboriginal communities in Australia. In these Aboriginal communitieswith high prevalence of uncontrolled Division of Nephrology, Department of Medicine, University of California, San Francisco, California