When should clinical guidelines be updated?

Considerable resources are being expended internationally on the development of clinical practice guidelines.1 Although consensus is increasing about methods for developing evidence based guidelines,2 less attention has been paid to the process for assessing when guidelines should be updated. The most common advice is for guidelines to include a scheduled review date. This could result in wasted resources, however, if a full update is undertaken prematurely in a slowly evolving field, or in guidelines in a rapidly evolving field becoming out of date before the scheduled review. Some guidelines state that they should be updated when new information becomes available. It is unclear, however, how this should be done, and we are unaware of any systematic attempts to devise a method. In this paper we propose a set of principles and a pragmatic model for assessing whether guidelines need to be updated. #### Summary points Changes in evidence, the values placed on evidence, the resources available for health care, and improvements in current performance are all possible reasons for updating clinical guidelines The need for an efficient mechanism for identifying when guidelines require updating is urgent A possible model for assessing validity of guidelines is based on a combination of multidisciplinary expert opinion and limited literature searches ### Changes in evidence on the existing benefits and harms of interventions New information about the magnitude of benefits and harms may make the pre-existing guideline invalid. The surgical risk of carotid endarterectomy, for example, has fallen substantially over the past 30 years, altering the risk-benefit ratio in favour of performing the operation for selected patients with symptomatic, high grade carotid stenosis.3–5 ### Changes in outcomes considered important New evidence may identify as important outcomes that were previously unappreciated or wholly unrecognised. Quality of life, for example, an end point often not considered in earlier research and guidelines, is receiving increasing …