title: Using patient management as a surrogate for patient health outcomes in diagnostic test evaluation.
abstract: BACKGROUND
  Before a new test is introduced in clinical practice, evidence is needed to demonstrate that its use will lead to improvements in patient health outcomes. Studies reporting test accuracy may not be sufficient, and clinical trials of tests that measure patient health outcomes are rarely feasible. Therefore, the consequences of testing on patient management are often investigated as an intermediate step in the pathway. There is a lack of guidance on the interpretation of this evidence, and patient management studies often neglect a discussion of the limitations of measuring patient management as a surrogate for health outcomes.
  
  
  METHODS
  We discuss the rationale for measuring patient management, describe the common study designs and provide guidance about how this evidence should be reported.
  
  
  RESULTS
  Interpretation of patient management studies relies on the condition that patient management is a valid surrogate for downstream patient benefits. This condition presupposes two critical assumptions: the test improves diagnostic accuracy; and the measured changes in patient management improve patient health outcomes. The validity of this evidence depends on the certainty around these critical assumptions and the ability of the study design to minimise bias. Three common designs are test RCTs that measure patient management as a primary endpoint, diagnostic before-after studies that compare planned patient management before and after testing, and accuracy studies that are extended to report on the actual treatment or further tests received following a positive and negative test result.
  
  
  CONCLUSIONS
  Patient management can be measured as a surrogate outcome for test evaluation if its limitations are recognised. The potential consequences of a positive and negative test result on patient management should be pre-specified and the potential patient benefits of these management changes clearly stated. Randomised comparisons will provide higher quality evidence about differences in patient management using the new test than observational studies. Regardless of the study design used, the critical assumption that patient management is a valid surrogate for downstream patient benefits or harms must be discussed in these studies.
authors.affiliation: NHMRC Clinical Trials Centre, The University of Sydney, Sydney, Australia. lukas.staub@ctc.usyd.edu.au
authors.forename: Lukas P
authors.initials: LP
authors.lastname: Staub
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Lord
authors.forename: R John
authors.initials: RJ
authors.lastname: Simes
authors.forename: Suzanne
authors.initials: S
authors.lastname: Dyer
authors.forename: Nehmat
authors.initials: N
authors.lastname: Houssami
authors.forename: Robert Y M
authors.initials: RY
authors.lastname: Chen
authors.forename: Les
authors.initials: L
authors.lastname: Irwig
mesh_terms: D015982:Bias; D003661:Decision Support Techniques; D003955:Diagnostic Tests, Routine / Q000379:methods / Q000592:standards*; D055317:Evidence-Based Practice; D006801:Humans; D017063:Outcome Assessment, Health Care; D010347:Patient Care Planning; D017410:Practice Guidelines as Topic; D015397:Program Evaluation; D011785:Quality Assurance, Health Care; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results; D012107:Research Design / Q000592:standards