Applying Class of Recommendations and Level of Evidence to Clinical Strategies, Interventions, Treatments, or Diagnostic Testing in Patient Care*

CLASS (STRENGTH) OF RECOMMENDATION
CLASS I (STRONG) Benefit >>> Risk
Suggested phrases for writing recommendations: Is recommended Is indicated/useful/effective/beneficial Should be performed/administered/other Comparative-Effectiveness Phrases†: Treatment/strategy A is recommended/indicated in preference to treatment B Treatment A should be chosen over treatment B
CLASS IIa (MODERATE) Benefit >> Risk
Suggested phrases for writing recommendations: Is reasonable Can be useful/effective/beneficial Comparative-Effectiveness Phrases†: Treatment/strategy A is probably recommended/indicated in preference to treatment B It is reasonable to choose treatment A over treatment B
CLASS IIb (WEAK) Benefit ≥ Risk
Suggested phrases for writing recommendations: May/might be reasonable May/might be considered Usefulness/effectiveness is unknown/unclear/uncertainor not well established
CLASS III: No Benefit (MODERATE) Benefit = Risk(Generally, LOE A or B use only)
Suggested phrases for writing recommendations: Is not recommended Is not indicated/useful/effective/beneficial Should not be performed/administered/other
CLASS III: Harm (STRONG) Risk > Benefit
Suggested phrases for writing recommendations: Potentially harmful Causes harm Associated with excess morbidity/mortality Should not be performed/administered/other
LEVEL (QUALITY) OF EVIDENCE‡
Level A
High-quality evidence‡ from more than 1 RCTs Meta-analyses of high-quality RCTs One or more RCTs corroborated by high-quality registry studies
Level B-R (Randomized)
Moderate-quality evidence‡ from 1 or more RCTs Meta-analyses of moderate-quality RCTs
Level B-NR (Nonrandomized)
Moderate-quality evidence‡ from 1 or more well-designed, well-executed nonrandomized studies, observational studies, or registry studies Meta-analyses of such studies
Level C-LD (Limited Data)
Randomized or nonrandomized observational or registry studies with limitations of design or execution Meta-analyses of such studies Physiological or mechanistic studies in human subjects
Level C-EO (Expert Opinion)
Consensus of expert opinion based on clinical experience
COR and LOE are determined independently (any COR may be paired with any LOE). A recommendation with LOE C does not imply that the recommendation is weak. Many important clinical questions addressed in guidelines do not lend themselves to clinical trials. Although RCTs are unavailable, there may be a very clear clinical consensus that a particular test or therapy is useful or effective. * The outcome or result of the intervention should be specified (an improved clinical outcome or increased diagnostic accuracy or incremental prognostic information). † For comparative-effectiveness recommendations (COR I and IIa; LOE A and B only), studies that support the use of comparator verbs should involve direct comparisons of the treatments or strategies being evaluated. ‡ The method of assessing quality is evolving, including the application of standardized, widely used, and preferably validated evidence grading tools; and for systematic reviews, the incorporation of an Evidence Review Committee. COR indicates Class of Recommendation; EO, expert opinion; LD, limited data; LOE, Level of Evidence; NR, nonrandomized; R, randomized; and RCT, randomized controlled trial.