Using patient management as a surrogate for patient health outcomes in diagnostic test evaluation

Abstract

BackgroundBefore 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.MethodsWe discuss the rationale for measuring patient management, describe the common study designs and provide guidance about how this evidence should be reported.ResultsInterpretation 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.ConclusionsPatient 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.

Cell cycle progression score and treatment decisions in prostate cancer: results from an ongoing registry

“…Decision impact surveys are an accepted form of analysis for the clinical utility of diagnostic tests and were recently reviewed by Staub et al 23 . The level of impact on patient care is recognized as Level III in the Fryback & Thornbury model for diagnostic test efficacy 24 .…”

Reply:

“…To date, there are no accepted guidelines for the design, reporting, and appraisal of patient-management studies. 12 In conclusion, we believe that the design of this well-controlled clinical trial provides valuable information on the 2 GBCAs. First, it demonstrates that gadobenate is significantly superior to gadoterate for qualitative and quantitative enhancement of brain lesions when these agents are administered at an equivalent dose of 0.1 mmol/kg of body weight.…”

The efficacy of bedside chest ultrasound: from accuracy to outcomes

“…Clinical decision-making involves diagnostic thinking efficacy and therapeutic efficacy. These levels of efficacy relate to the cognitive impact of the test result on clinician behaviour [10]. Diagnostic thinking efficacy describes the usefulness of a test to influence a clinician's thinking.…”

“…Some degree of diagnostic accuracy is usually required to change clinician decision-making, which in turn is needed to improve final patient outcomes [10]. Of course, diagnostic accuracy does not always change decision-making, nor do changes in medical decision-making automatically confer outcome efficacy [12].…”