Cohort studies: to what extent can they inform treatment guidelines?

This review examines situations in which information from cohort studies has proved to be useful for the development of treatment guidelines.

Although there are several reasons why randomized controlled trials (RCTs) are felt to provide the most robust evidence for treatment guidelines, they may suffer from insufficient duration of follow-up, inadequate power to consider differences in important adverse events and highly selected patient populations. Furthermore, as most RCTs are performed for licensing purposes, strategic treatment decisions often lack supportive evidence from RCTs. Although data from cohort studies may be used to complement information from RCTs, cohort studies themselves are susceptible to several biases (most notably confounding) which may limit their findings. However, in the HIV field, information from such studies has been influential in guiding decisions relating to when to start highly active antiretroviral therapy, what drugs to use in the initial highly active antiretroviral therapy regimen and when to switch highly active antiretroviral therapy should virological failure occur.

Given the biases that may be present, caution should be exercised when interpreting findings from cohort studies, particularly if comparisons are made of treatment strategies that involve some element of patient or clinician choice.