Table 1 Evidence-based rating system used in the hematopoietic cell transplantation (HCT) guidelines²

Strength of recommendation

 A

Both strong evidence for efficacy and substantial clinical benefit support recommendation for use. Should always be offered

 B

Moderate evidence for efficacy—or strong evidence for efficacy, but only limited clinical benefit—supports recommendation for use. Should generally be offered.

 C

Evidence for efficacy is insufficient to support a recommendation for or against use, or evidence for efficacy might not outweigh adverse consequences (for example, drug toxicity, drug interactions) or cost of the chemoprophylaxis or alternative approaches. Optional.

 D

Moderate evidence for lack of efficacy or for adverse outcome supports a recommendation against use. Should generally not be offered.

 E

Good evidence for lack of efficacy or for adverse outcome supports a recommendation against use. Should never be offered.

Quality of evidence supporting the recommendation

 I

Evidence from at least one well-executed, randomized, controlled trial.

 II

Evidence from at least one well-designed clinical trial without randomization; cohort or case–controlled analytic studies (preferably from more than one center); multiple time-series studies; or dramatic results from uncontrolled experiments.

 III

Evidence from opinions of respected authorities based on clinical experience, descriptive studies or reports of expert committees.