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Pignone MP, Phillips CJ, Lannon CM, et al. Screening for Lipid Disorders [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2001 Apr. (Systematic Evidence Reviews, No. 4.)

  • This publication is provided for historical reference only and the information may be out of date.

This publication is provided for historical reference only and the information may be out of date.

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Screening for Lipid Disorders [Internet].

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2Methods

This chapter of the systematic evidence review (SER) documents the procedures that the RTI-UNC Evidence-based Practice Center (EPC) used to develop this report on screening for lipid disorders among adults and children. We document the literature search (eg, inclusion and exclusion criteria, relevant Medical Subject Headings [MeSH terms]) and briefly describe the procedures followed in abstracting data from included articles, developing evidence tables, analyzing the literature, and subjecting the draft to a robust peer review process. The EPC followed procedures established by the USPSTF Methods Work Group.27

In all these steps, EPC staff collaborated with 2 members of the US Preventive Services Task Force (USPSTF) who acted as liaisons for this topic; they are coauthors of this SER. The collaboration took place chiefly by electronic mail and numerous conference calls. Steps in the development of this SER were presented at USPSTF meetings in February, May, and September 1999 and February 2000 where the EPC staff and Task Force liaisons also were able to discuss the analytic framework and key clinical questions (linkages), literature search strategy, results, and implications of the findings.

Literature Search Strategy

Inclusion/Exclusion Criteria

To identify articles relevant to the questions of screening and treatment of lipid disorders, the EPC staff searched the MEDLINE database from 1994 to December 1999. The searches focused on 4 main areas: drug therapy for lipid disorders, diet and exercise therapy for lipid disorders, screening, and harms and adverse events. Drug and diet or exercise treatments correspond to Key Question Nos. 1 and 2 in the analytic framework; screening corresponds to Key Question No. 3.

We prospectively established inclusion and exclusion criteria for all searches. Table 1 presents the overall and specific criteria for each of the 4 main searches (on drug therapy, diet therapy, screening, and harms and adverse effects). Table 2 documents the results of the 4 main literature searches.

Table 1. Screening for Lipid Disorders: Inclusion and Exclusion Criteria.

Table

Table 1. Screening for Lipid Disorders: Inclusion and Exclusion Criteria.

Table 2. Screening for Lipid Disorders: Search Strategy Results.

Table

Table 2. Screening for Lipid Disorders: Search Strategy Results.

We supplemented our searches with a check of the Cochrane database of controlled trials to identify important articles not included in MEDLINE.28 We used the second edition of the USPSTF Guide to Clinical Preventive Services 12(as well as systematic reviews, meta-analyses, and evidence-based practice guidelines that addressed screening and treatment of lipid disorders(to identify key articles that were published before 1994. We also identified and used several large, prospective observational studies to answer contextual questions about screening. Finally, we hand-searched bibliographies of included articles to detect any important articles that may have been missed in the other steps. Table 2 documents the results of the 4 main literature searches.

Literature Reviewed

Two EPC staff independently reviewed the titles and abstracts of the articles identified by the literature searches and excluded ones that they agreed clearly did not meet eligibility criteria. When the initial reviewers disagreed or were uncertain, the articles were carried forward to the next review stage, in which the EPC team members reviewed the full articles and made a final decision about inclusion or exclusion by consensus. Table 3 summarizes the results of the literature searches and reviews of abstracts. The literature searches concerning the 3 key clinical questions (linkages in the analytic framework) are described in more detail just following, as is the specific search strategy to identify adverse events.

Table 3. Summary Results from Literature Searches and Reviews.

Table

Table 3. Summary Results from Literature Searches and Reviews.

Drug Interventions

With respect to drug therapies (Key Question No. 1), we examined randomized trials of at least 1-year duration that used pharmacologic agents and that reported coronary heart disease (CHD) outcomes. We specifically excluded estrogen, which will be considered in a separate review, and we chose not to examine dietary supplements. Neither estrogen nor dietary supplements have been studied in trials that would meet our criteria, however. We identified 475 articles from our main literature searches and added 41 other publications through supplemental searches. Of these 516 articles, we rejected 448 at the stage of reviewing abstracts and selected 68 for full article review. Of these 68, we found that 34 examined trials of secondary prevention and were thus excluded.

Two abstractors reviewed each of the 34 remaining articles and assessed them for appropriateness as defined in the eligibility criteria; we excluded 12 articles at this stage (these are documented in Appendix 1, Table 1.1).29 - 41 The remaining 22 articles were then either fully abstracted for the evidence tables (4 articles) or used for supplementary information (18 articles). We collected standard information on the study design, intervention, and results; in addition, we rated the quality of the articles based on their internal and external validity. Internal validity was assessed with respect to 4 markers: adequate inclusion criteria, adequate randomization and concealment, nondifferential loss to follow-up, and use of intention-to-treat analysis (see Appendix 2).27

Dietary and Exercise Interventions

For Key Question No. 2 about the use of dietary and exercise therapy for lipid disorders, our initial literature searches identified 300 articles from the MEDLINE database for the years 1995 to 1999 (Table 3). We added 215 articles through supplementary searches, including 108 about the effects of exercise on lipids (based on a request from the full USPSTF). In our initial review of the abstracts, we excluded 425 articles that did not meet eligibility criteria, leaving 90 articles for full review. Two abstractors reviewed each of the remaining articles and assessed them for appropriateness as defined in the eligibility criteria; we excluded 51 articles at this stage (see Appendix 1, Table 1.2).42 - 90 The final 39 articles concerning dietary interventions and lipids were then either fully abstracted (14 articles) or used to provide supplementary information (25 publications). The diet and exercise searches included articles that measured changes in lipid levels only because these interventions are often considered for patients such as children or young adults who have low short-term risk for CHD events. We also chose not to examine the effect of particular dietary supplements such as garlic or oat bran.

In addition to the elements abstracted for drug therapy, we also rated the intensity of the dietary intervention as low, medium, or high to aid in evaluation of generalizability. Low-intensity interventions took place in 1 session less than 30 minutes in duration and did not require ongoing data collection by the patient (such as a food diary); high-intensity interventions required multiple sessions (6 or more) and considerable data collection and recordkeeping; and medium-intensity interventions fell in between. We assessed study quality in terms of internal validity according to the same criteria used for drug therapy.

Screening Literature

For Key Question No. 3, the subject headings of mass screening, diagnostic use, and sensitivity and specificity were crossed with cholesterol and hyperlipidemia, generating 177 references from 1994 to 1999. We evaluated these abstracts as well as another 40 from our supplemental searching. On the basis of review at this stage, we excluded 150 articles and retained 67 that appeared to be appropriate and useful. We then used these 67 articles to examine the accuracy, reliability, feasibility, and acceptability of screening.

Harms and Adverse Events

At the initial literature search stage, we identified a possible 133 articles specifically concerning this topic; to this set we added 140 articles from various supplemental searches. Of the 273 abstracts reviewed, we excluded 181 items, leaving 92 publications for full review of the entire article. After evaluation of the full articles, we retained 25 and used them to create sections of the results associated with drug therapy, diet therapy, and screening; information in 21 of these 25 articles appears in specific harms tables.

Literature Synthesis and Preparation of Systematic Evidence Review

Data Abstraction and Development of Evidence Tables

We entered study design and outcomes data from the articles on drug and diet treatment into an electronic database (Microsoft Access91); we constructed evidence tables in Microsoft Excel and Word.92 , 93

To characterize the quality of the included studies, we rated the internal and external validity for each article in the evidence tables using criteria developed by the USPSTF Methods Work Group. We then rated the aggregate internal validity and external validity as well as the coherence (agreement of the results of the individual studies) for each of the Key Questions defined in the analytic framework. The quality rating scales developed by the Methods Work Group are included in Appendix 2.27

Meta-analysis

To better estimate the effects of drug therapy, we performed a quantitative meta-analysis under both random and fixed effects models using RevMan software.94 The methods and results of this analysis are briefly described here and documented more fully in a separate paper.95 We examined the effect of drug therapy on the incidence of CHD events (nonfatal myocardial infarction and CHD deaths combined), on the incidence of CHD deaths alone, and on total mortality. We represented the results as summary odds ratios with 95% confidence intervals and examined the results for heterogeneity visually and using tests of homogeneity. We also performed subanalyses that measured the effect of the statin drugs alone, which included 4 studies that could not be clearly included or excluded based on our prospective eligibility criteria.

Peer Review Process

On completion of a draft SER, we conducted a broad-based, external review of the draft. Among the outside reviewers were representatives of key primary care professional associations that have formal liaison ties to the USPSTF, a representative of the Canadian Task Force on Preventive Health Care, representatives of other professional societies, clinical experts in the area of cardiovascular disease and lipid disorders, members of the staff of the Agency for Healthcare Research and Quality, and representatives of other relevant federal agencies. The names and affiliations of all peer reviewers are listed on page iv. We took account of all substantive comments from reviewers in developing the final version of this SER.

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