Level of Evidence Used in Infectious Diseases Society of America Practice Guidelines

Clinical practice guidelines have been developed to help clinicians improve patient outcomes and to streamline delivery of healthcare by analyzing and summarizing data from relevant publications. Guidelines are also utilized as educational tools, measure of performance, and policy making. Physicians generally assume that use of clinical practice guidelines means practicing evidence-based medicine, but, according to researchers, the quality of supporting literature can vary greatly. The researchers recently designed an analysis to assess the overall quality of evidence behind the recommendations outlined in existing guidelines from the Infectious Diseases Society of America (IDSA). They reported results in Archives of Internal Medicine [2011;171(1):18-22]. The guidelines use the IDSA-US Public Health Service grading system (IDSA evidence-grading system), where each recommendation is graded according to its strengths and the underlying quality of evidence. Strengths range from A (good evidence to support recommendation for use), to B (moderate evidence to support recommendation), to C (poor evidence to support recommendation). Some guidelines, released mostly prior to 2008, included level D (moderate evidence to support recommendation against use) and E (good evidence to support recommendation against use). Quality of evidence ranges from level I (evidence from ≥1 properly randomized controlled trial) to level II (evidence from ≥1 well-designed, clinical trial, without randomization, from cohort or case-controlled analytical studies or from dramatic results from uncontrolled experiments) to level III (evidence from opinions of respected authorities based on clinical experience, descriptive studies, or reports of expert committees). The researchers compared 5 recently published IDSA guidelines that were updated between January 2008 and May 2010 with their respective older versions. They analyzed data on the percentage of new references and on the total number of individual recommendations as well as the number of level I, II, and III quality-of-evidence designations for each of the 5 guideline pairs. As of May 2010, there are 52 current guidelines listed in the IDSA Web site. Of these, 41 used the IDSA evidence-grading system for individual recommendations. Of those 41 guidelines, 51% (n=21) covered a new topic and 49% (n=24) were updates of earlier published versions (2 of the guidelines had been updated twice). On further analysis, the researchers found 4128 individual recommendations that they charted according to strength of recommendation and quality of evidence. Only 14% (n=603) were linked to level I evidence; 31% (n=1307) were classified as level II, and 55% (n=2330) as level III evidence. Analysis of all level A strength recommendations (n=1796) revealed that 23% (n=414) were supported by level I quality of evidence, 40% (n=715) were based on level II evidence, and 37% (n=667) were based on level III. Although the updated guidelines expanded the absolute number of individual recommendations substantially, few were due to a sizable increase in level I evidence. The majority of additional recommendations were based on level II and level III evidence. Study limitations cited by the authors include not analyzing all current IDSA guidelines, lacking evaluation of the primary cited literature, and limiting the study to the guidelines published by the IDSA. In summary, the researchers noted that, “more than half of the current recommendations of the IDSA are based on level III evidence only. Until more data from well-designed controlled clinical trials become available, physicians should remain cautious when using current guidelines as the sole source guiding patient care decisions.”