Manual for ACC/AHA Guideline Writing Committees
Methodologies and Policies from the ACC/AHA Task Force on Practice Guidelines
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Section II: Tools and Methods for Creating Guidelines
- Step Six: Assign Classification of Recommendations and Level of Evidence
Once recommendations are written, a Classification of Recommendation and Level of Evidence grade must be assigned to each recommendation. Classification of Recommendations and Level of Evidence are as follows:
Classification of Recommendations
| Class I: | Conditions for which there is evidence and/or general agreement that a given procedure or treatment is useful and effective. | |
| Class II: | Conditions for which there is conflicting evidence and/or a divergence of opinion about the usefulness/efficacy of a procedure or treatment. | |
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IIa. Weight of evidence/opinion is in favor of usefulness/efficacy |
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| Class III: | Conditions for which there is evidence and/or general agreement that the procedure/treatment is not useful/effective, and in some cases may be harmful. |
Level of Evidence
| Level of Evidence A | Data derived from multiple randomized clinical trials | |
| Level of Evidence B | Data derived from a single randomized trial, or non-randomized studies | |
| Level of Evidence C |
Consensus opinion of experts |
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Like the collection and quality analysis of scientific data from an experimental study, collection and grading of the evidence for guideline development allow conclusions (ie, guideline recommendations) to be developed in a manner that is supportable by the data (ie, scientific evidence in the literature). - Heffner, 1998 |
Applying
the Classifications and Levels
Some writers prefer to assign the Classification of Recommendation
and Level of Evidence when writing the recommendations, while
others prefer to state the recommendation and assign the classification
later after re-examining the data. Writers preferring the
first method will conduct Steps
Five and Six
of the guideline methodology simultaneously.
The Classification of Recommendations and Level of Evidence are considered by many to be the core of the guidelines. As such, they are among the most debated aspects of the guideline within the writing group. See Step Eight for guidance on coming to group consensus on recommendations.
Table 3: Applying Classification of Recommendations and Level of Evidence provides more descriptive and quantitative criteria for assigning the classification and evidence ratings. Additionally, it displays the intersections between each rating. Any combination of Classification of Recommendation and Level of Evidence is possible. For example, a recommendation can have a Class I, even if it is based entirely on expert opinion and no research studies have ever been conducted on the recommendation (Level C). Similarly, a Class IIa or IIb can be assigned a Level A if there are multiple randomized controlled trials coming to divergent conclusions.
Assigning a Level of Evidence B or C should not be construed as implying that the recommendation is weak. Many important clinical questions addressed in the guidelines either do not lend themselves to experimentation or have not yet been addressed by high quality investigations. Even though randomized controlled trials may not be available, the clinical question may be so relevant that it would be delinquent to not include it in the guideline.
Table 3. Applying Classification of Recommendations and Level of Evidence
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Class I | Class IIa | Class IIb | Class III | |
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Benefit >>> Risk Procedure/Treatment SHOULD be performed/ administered |
Benefit >> Risk IT IS REASONABLE to perform procedure/ administer treatment |
Benefit≥
Risk IT IS NOT UNREASONABLE to perform procedure/ administer treatment |
Risk
≥ Benefit Procedure/Treatment should NOT be performed/ administered SINCE IT IS NOT HELPFUL AND MAY BE HARMFUL |
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Level A Multiple (3-5) population risk strata evaluated General consistency of direction and magnitude of effect |
o Recommendation that procedure or treatment is useful/effective o Sufficient evidence from multiple randomized trials or meta-analyses |
o Recommendation in favor of treatment or procedure being useful/effective o Some conflicting evidence from multiple randomized trials or meta-analyses |
o Recommendation's usefulness/efficacy less well established o Greater conflicting evidence from multiple randomized trials or meta-analyses |
o Recommendation that procedure or treatment not useful/effective and may be harmful o Sufficient evidence from multiple randomized trials or meta-analyses |
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Level B Limited (2-3) population risk strata evaluated |
o Recommendation that procedure or treatment is useful/effective o Limited evidence from single randomized trial or non-randomized studies |
o Recommendation in favor of treatment or procedure being useful/effective o Some conflicting evidence from single randomized trial or non-randomized studies |
o Recommendation's usefulness/efficacy less well established o Greater conflicting evidence from single randomized trial or non-randomized studies |
o Recommendation that procedure or treatment not useful/effective and may be harmful o Limited evidence from single randomized trial or non-randomized studies |
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Level C Very limited (1-2) population risk strata evaluated |
o Recommendation that procedure or treatment is useful/effective o Only expert opinion, case studies, or standard-of-care |
o Recommendation in favor of treatment or procedure being useful/effective o Only diverging expert opinion, case studies, or standard-of-care |
o Recommendation's usefulness/efficacy less well established o Only diverging expert opinion, case studies, or standard-of-care |
o Recommendation that procedure or treatment not useful/effective and may be harmful o Only expert opinion, case studies, or standard-of-care |
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