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

Staub LP, Lord SJ, Simes RJ, Dyer S, Houssami N, Chen RY, Irwig L - BMC Med Res Methodol (2012)

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: NHMRC Clinical Trials Centre, The University of Sydney, Sydney, Australia. lukas.staub@ctc.usyd.edu.au

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.

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Test-treatment pathway showing Accuracy, Impact on management and Treatment effectiveness as determinants of health outcomes. Adapted from Staub et al. [9]
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Figure 1: Test-treatment pathway showing Accuracy, Impact on management and Treatment effectiveness as determinants of health outcomes. Adapted from Staub et al. [9]

Mentions: The Fryback and Thornbury framework [10] recognises that medical tests are embedded in a clinical pathway. We use a simplified version of the clinical pathway, referred to here as the 'test-treatment pathway', to illustrate the key concepts (Figure 1). This pathway is characterised by the population who will be tested, and the available tests and management options. It shows that when a test is claimed to improve patient health outcomes by improving management decisions, the key determinants are test accuracy for detecting cases eligible for a change in management and the effectiveness of the management. Measuring patient management as a surrogate outcome involves specifying what changes in management will occur that are expected to benefit patients, rather than measuring overall changes in management. The proposed role of a test within the pathway, that is whether it will be used as a replacement for an existing test, as an add-on after existing tests, or before as a triage test to achieve this claim also needs to be stated [12].


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

Staub LP, Lord SJ, Simes RJ, Dyer S, Houssami N, Chen RY, Irwig L - BMC Med Res Methodol (2012)

Test-treatment pathway showing Accuracy, Impact on management and Treatment effectiveness as determinants of health outcomes. Adapted from Staub et al. [9]
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3313870&req=5

Figure 1: Test-treatment pathway showing Accuracy, Impact on management and Treatment effectiveness as determinants of health outcomes. Adapted from Staub et al. [9]
Mentions: The Fryback and Thornbury framework [10] recognises that medical tests are embedded in a clinical pathway. We use a simplified version of the clinical pathway, referred to here as the 'test-treatment pathway', to illustrate the key concepts (Figure 1). This pathway is characterised by the population who will be tested, and the available tests and management options. It shows that when a test is claimed to improve patient health outcomes by improving management decisions, the key determinants are test accuracy for detecting cases eligible for a change in management and the effectiveness of the management. Measuring patient management as a surrogate outcome involves specifying what changes in management will occur that are expected to benefit patients, rather than measuring overall changes in management. The proposed role of a test within the pathway, that is whether it will be used as a replacement for an existing test, as an add-on after existing tests, or before as a triage test to achieve this claim also needs to be stated [12].

Bottom Line: 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: NHMRC Clinical Trials Centre, The University of Sydney, Sydney, Australia. lukas.staub@ctc.usyd.edu.au

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.

Show MeSH
Related in: MedlinePlus