Use of surrogate outcomes in cost-effectiveness models: a review of United Kingdom health technology assessment reports.

OBJECTIVES: The aim of this study was to explore the use of surrogate outcomes--a substitute outcome that predicts final patient-related outcomes--in cost-effectiveness models (CEM) within health technology assessment (HTA) reports and provide guidance for their future use.
METHODS: Our sampling frame was all UK HTA Program monograph series reports published in 2005 and 2006. Reports were included if they addressed a treatment effectiveness/efficacy question and included a CEM based on a surrogate outcome. The two authors independently applied inclusion and exclusion criteria, and the following data was extracted from included reports: source of surrogate outcome, level of evidence for validation of the surrogate outcomes, methods used in report to quantify link between surrogate outcome and final outcome, and consideration of the uncertainty associated with using surrogate outcomes in the results or conclusions of report.
RESULTS: Of 100 HTA reports, 35 complied with the inclusion criteria. Of these, four (11 percent) reports included a CEM based on a surrogate outcome. All four reports sourced treatment-related changes in surrogate outcome through a systematic review of the literature. One provided Level 1 surrogate evidence (randomized controlled trial data showing a strong association between the change in surrogate outcome and change final outcome); two reported Level 2 evidence (observational study data); and one provided Level 3 evidence (disease natural/ history data). The transparency of quantification and exploration of uncertainty of the surrogate and final outcome relationship varied considerably across all four reports.
CONCLUSIONS: Recommendations are made for the use of surrogate outcomes in future HTA reports.