Linking the evidence: intermediate outcomes in medical test assessments

Objectives: The aim of this study is to review how health technology assessments (HTA) of medical tests incorporate intermediate outcomes in conclusions about the effectiveness of tests on improving health outcomes. Methods: Systematic review of English-language test assessments in the HTA database from January 2005 to February 2010, supplemented by a search of the Web sites of International Network of Agencies for Health Technology Assessment (INAHTA) members. Results: A total of 149 HTAs from eight countries were assessed. Half evaluated tests for screening or diagnosis, a third for disease classification (including staging, prognosis, monitoring), and a fifth for multiple purposes. In seventy-one HTAs (48 percent) only diagnostic accuracy was reported, while in seventeen (11 percent) evidence of health outcomes was reported in addition to accuracy. Intermediate outcomes, mainly the impact of test results on patient management, were considered in sixty-one HTAs (41 percent). Of these, forty-seven identified randomized trials or observational studies reporting intermediate outcomes. The validity of these intermediate outcomes as a surrogate for health outcomes was not consistently discussed; nor was the quality appraisal of this evidence. Clear conclusions about whether the test was effective were included in approximately 60 percent of HTAs. Conclusions: Intermediate outcomes are frequently assessed in medical test HTAs, but interpretation of this evidence is inconsistently reported. We recommend that reviewers explain the rationale for using intermediate outcomes, identify the assumptions required to link intermediate outcomes and patient benefits and harms, and assess the quality of included studies.