Craig Fleming

Screening for abdominal aortic aneurysm: A best-evidence systematic review for the U.S. Preventive Services Task Force

An abdominal aortic aneurysm (AAA) occurs when the aorta below the renal arteries expands to a maximal diameter of 3.0 cm or greater. Abdominal aortic aneurysms are found in 4% to 8% of older men and 0.5% to 1.5% of older women (1-5). Age, smoking, sex, and family history are the most significant AAA risk factors (1). Aortic aneurysms account for about 15000 deaths in the United States annually; of these, 9000 are AAA-related and the remainder are due to thoracic aortic aneurysms (6, 7). Most AAA deaths occur in men 65 years of age and older (8, 9). Although AAAs may be asymptomatic for years, as many as 1 in 3 eventually rupture if left untreated (10). The prognosis for ruptured AAAs is grim. Since most patients with ruptured AAAs die out of the hospital or before surgery (11), and since the operative mortality rate for emergent AAA repair is high (12), only 10% to 25% of individuals with ruptured AAAs survive until hospital discharge. Ultrasonography of the abdomen is accurate (13, 14) and reliable (15) in detecting AAAs. Survival after elective surgical repair approaches that of the general population (16). Elective AAA repair, however, may result in significant harms, such as operative mortality, myocardial infarction, respiratory and renal failure, and changes in functional status (17, 18). In its 1996 recommendation, the U.S. Preventive Services Task Force (USPSTF) found insufficient evidence to recommend for or against routine AAA screening of asymptomatic adults. The Task Force cited the need for data from population-based screening trials to determine whether the potential benefit from preventing ruptured AAAs justified the potential risks from increased surgery (19). Since 1996, results from 4 population-based randomized, controlled trials of AAA screening have been published (5, 9, 20-24). On the basis of this new evidence, the USPSTF sought to update its 1996 recommendation by reassessing the benefits and harms of population-based AAA screening. This systematic review was performed by investigators from the Oregon Evidence-based Practice Center, Portland, Oregon, in collaboration with the USPSTF and the Agency for Healthcare Research and Quality, Rockville, Maryland. Descriptions of the analytic framework, key questions, literature search, inclusion criteria, data extraction methods, quality rating, and trial flow diagram are provided in the Appendix, Appendix Figures 1 and 2, and the Appendix Table. The evidence review focused on the following key questions: 1a) Does AAA screening, in an asymptomatic average-risk or high-risk population, reduce AAA-related adverse health outcomes? 1b) For individuals who do not have AAAs on initial screening, does periodic repeated screening reduce AAA-related adverse health outcomes? 2) What are the harms associated with AAA screening? 3) For AAAs 3.0 to 5.4 cm detected through screening, does immediate repair or surveillance reduce AAA-related adverse health outcomes? 4) What are the harms associated with repair of AAAs 5.5 cm or greater? 5) What are the harms associated with immediate repair or surveillance of AAAs 3.0 to 5.4 cm? This article focuses only on key questions 1a, 1b, 2, and 4, which are most relevant to determining the net benefit (benefit minus harms) of population-based screening for AAA. Key questions 3 and 5 address management strategies for AAAs 3.0 to 5.4 cm, which are at much lower risk for rupture than larger AAAs (25, 26). Key questions 3 and 5 are reviewed in our full systematic evidence synthesis (available at www.preventiveservices.ahrq.gov). Methods We performed this review on the basis of methods previously established by the USPSTF (27). We initially developed an analytic framework and key questions, in conjunction with USPSTF liaisons, to define the strategy used to perform this systematic review. Since direct evidence regarding population-based screening from randomized, controlled trials was available, we did not explicitly review the accuracy and reliability of ultrasonography in population-based AAA screening. The sensitivity of ultrasound scanning for an AAA is 95%, and the specificity approaches 100%; the examination is safe and reliable (14, 15, 28, 29). Limited ultrasonography for AAA screening can be performed in less than 10 minutes (30). To identify relevant studies, we searched MEDLINE (January 1994 through July 2004), the Cochrane Database of Systematic Reviews (2004, Issue 1), and the Cochrane Controlled Trials Register (January 1994 through May 2004). Literature search strategies are summarized in the Appendix. We identified additional studies from the reference lists of retrieved articles, periodic hand searches of relevant journals, and suggestions from experts. To evaluate the effectiveness of AAA screening (key question 1a), we searched for randomized, controlled trials of population-based screening for AAA. To evaluate the benefit of periodic repeated screening after a normal scan (key question 1b), we identified cohort or follow-up studies of patients without AAAs identified in population screening studies. To evaluate the potential harms associated with AAA screening and treatment (key questions 2 and 4), we examined data from the trials of population screening and searched for other relevant retrospective or prospective cohort studies. Two authors reviewed 271 abstracts and 26 articles using defined inclusion criteria and abstracted relevant information about the population, setting, interventions, and outcomes of each included trial of screening and harms (see the Appendix and Appendix Figure 2 for inclusion criteria and the trial flow diagram). Predefined criteria from the USPSTF were used to assess the internal validity of each population-based screening trial and to assign quality ratings of good, fair, or poor (27). We did not assign quality ratings for studies of repeated screening or harms of screening and treatment. We used published data from the trials of population-based AAA screening to calculate estimates of unadjusted odds ratios (ORs) and 95% CIs for AAA-related mortality and all-cause mortality. We performed meta-analyses to calculate summary estimates for AAA-related mortality and all-cause mortality using the DerSimonian and Laird random-effects model (31). When no heterogeneity is present, the DerSimonian and Laird random-effects estimate is identical to the fixed-effects estimate. We deemed the random-effects model to be more appropriate than a fixed-effects model because the included studies differed in characteristics such as population, starting and stopping ages for screening, outcomes ascertainment, and duration of follow-up (32). We used graphs of trial outcomes and the MantelHaenszel chi-square test to assess heterogeneity. We used RevMan software (Reviewer Manager Version 4.2.2, 2003, The Cochrane Collaboration, Oxford, United Kingdom) to perform all statistical analyses. We modeled the impact of screening on AAA-related mortality over 5 years for 100000 U.S. men age 65 to 74 years. We also examined how the modeled impact of screening would differ in those with a history of smoking and those who had never smoked within this same sample. This article is based on a full evidence synthesis, which is available at www.preventiveservices.ahrq.gov. Role of the Funding Source This research was funded by the Agency for Healthcare Research and Quality under a contract to support the work of the U.S. Preventive Services Task Force. Agency staff and Task Force members participated in the initial design of the study and reviewed interim analyses and the final manuscript. The full evidence report was distributed for review to content experts and was revised accordingly. Agency approval was required before this manuscript could be submitted for publication, but the authors are solely responsible for its content and the decision to submit it. Data Synthesis Trial Characteristics We identified 4 randomized, controlled trials that evaluated population-based screening for AAA: the Multicentre Aneurysm Screening Study (MASS) from the United Kingdom (22); the Chichester, United Kingdom, screening study (5, 9, 20); the Viborg County, Denmark, screening study (21); and the Western Australia screening study (23, 33, 34). Table 1 shows the characteristics of the 4 screening trials. All trials identified potential participants age 65 years or older at average risk for AAA through population registries or regional health directories. The 4 trials included more than 125000 total participants. Different stopping ages were used for each trial and ranged from 73 years to 83 years. No data were provided on race or ethnicity. Only the Chichester trial included women. Table 1. Characteristics of Screening Trials for Abdominal Aortic Aneurysm In MASS and in the Chichester and Western Australia trials, participants were excluded before randomization if they resided in nursing homes. In MASS and in the Chichester trial, participants were also excluded before, and without knowledge of, randomization if their primary physician deemed them unfit for elective AAA repair. Participants were then randomly assigned to an intervention group that received an invitation to attend screening or to a control group that received usual care. All control group participants were followed passively and without contact. Across the 4 trials, 63% to 80% of invited participants attended ultrasound scanning. On an intention-to-treat basis, those who were invited to screening but did not attend were also included in the analysis. In MASS and in the Chichester and Viborg County trials, patients with AAAs exceeding a threshold size of 5.0 to 6.0 cm on initial measurement were referred to a vascular surgeon. Patients with smaller AAAs periodically underwent repeated scanning and were referred to a vascular surgeon for AAAs that had expanded to or above the threshold size. In MASS and in the Chichester trial, patients were also referred if the AA

Screening for primary open-angle glaucoma in the primary care setting: an update for the US preventive services task force.

PURPOSE Primary open-angle glaucoma (POAG) is a leading cause of blindness and vision-related disability. This review examines the effectiveness of screening for and treatment of early POAG in asymptomatic persons. METHODS We identified studies of glaucoma screening and treatment from MEDLINE, the Cochrane Library, and glaucoma experts. Two reviewers abstracted relevant studies and graded articles according to US Preventive Services Task Force criteria. RESULTS No randomized, controlled trials of population screening for POAG have been reported. Two randomized controlled trials compared the efficacy of treatment to lower intraocular pressure with no treatment for persons who have early primary open-angle glaucoma. In a Swedish trial, treatment reduced progression at 5 years from 62% without treatment to 45% with treatment (absolute risk reduction [ARR] 17%, number needed to treat 5.8, P = .007). In a US trial of patients with early POAG and normal intraocular pressure, progression at 5 years was observed in 39% of those without treatment and 33% of those with treatment (P = .21). The benefit of delaying progression of visual field loss on vision-related function in patients with early POAG is unclear. The principal harm of treatment is loss of visual acuity resulting from an increased risk of cataract formation. CONCLUSIONS Treatment to lower intraocular pressure may delay progression of visual field deficits in some asymptomatic individuals with early POAG. Further studies of population screening are needed to show that early recognition and treatment of glaucoma in asymptomatic patients are effective in improving vision-specific functional outcomes and health-related quality of life.