Table 2.

Applying American College of Cardiology/American Heart Association Class of Recommendation and Level of Evidence to Clinical Strategies, Interventions, Treatments, or Diagnostic Testing in Patient Care^* (Updated May 2019)

CLASS (STRENGTH) OF RECOMMENDATION
CLASS 1 (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 2a (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 2b (WEAK)	Benefit ≥ Risk
Suggested phrases for writing recommendations:  • May/might be reasonable  • May/might be considered  • Usefulness/effectiveness is unknown/unclear/uncertain or not well-established
CLASS 3: No Benefit (MODERATE) (Generally, LOE A or B use only)	Benefit = Risk
Suggested phrases for writing recommendations:  • Is not recommended  • Is not indicated/useful/effective/beneficial  • Should not be performed/administered/other
Class 3: Harm (STRONG)	Risk > Benefit
Suggested phrases for writing recommendations:  • Potentially harmful  • Causes harm  • Associated with excess morbidity/mortallty  • Should not be performed/administered/other
LEVEL (QUALITY) OF EVIDENCE ‡
LEVEL A
• High-quality evidence‡ from more than 1 RCT  • 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 he specified (an improved clinical outcome or increased diagnostic accuracy or incremental prognostic information).

^†For comparative-effectiveness recommendatiens (COR 1 and 2a; 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.