Assessment of Diagnostic Technology in Health Care Rationale, Methods, Problems, and Directions (1989) / Chapter Skim
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3. Assessment: Problems and Proposed Solutions
3. Assessment: Problems and Proposed Solutions
Pages 55-72
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From page 55... ...
Medical tests are more difficult to evaluate than medical treatments. A treatment is typically evaluated Pugh a clinical trial in which patients are randomly assigned to the treatment group or to a control group, which may receive a placebo or conventional therapy.
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From page 56... ...
scanner meets this cnter~on if it produces a crisp image of Me brain, regardless of whether mat image fairy reflects the true state of the brain. The Food and Drug Admit stration currency requires this level of assessment for diagnostic technologies before it win issue premarket~ng approval.
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From page 57... ...
But, as indicated In Chapter 2, a test may alter therapy in one patient but not in another, depending on the pretest probability and the treatment Reshoot. Impact on Clinical Outcomes The ultimate measure of a test is its ability to alter the patient's outlook by leading to changes in management that reduce symptoms or prolong life.
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From page 58... ...
These studies include a research question, which usually cans for the comparison of several technologies; they also include a rigorous study design and meticulous implementation of the study protocol. In studies of diagnostic technology, the index test, one or more competing tests, and a gold-standard test are performed in a series of patients.
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From page 59... ...
For example, published studies of diagnostic tests infrequency report clinical prediction rules for estimating pretest probability. Studies of technology often apply only to a narrow spectrum of patients.
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From page 60... ...
Studies of diagnostic tests often do not compare one test with a competing test. When competing tests are compared, the design of the study usually precludes a complete answer to such questions as, "Should ~ do Test A but not Test B?
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From page 61... ...
198S, NTH Consensus Conference 19881. We now turn to a discussion of how diagnostic tests should be evaluRANDOMIZED TRIALS OF DIAGNOSTIC TESTS A well-designed and well-executed randomized clinical trial is widely regarded as the most powerful method for comparing technologies.
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From page 62... ...
Randomized trials can be very costly if standardization of the intervention requires special care for patients. By focusing on effectiveness Measuring effects under usual patient care conditions)
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From page 63... ...
This advantage suggests two types of randomized trials of diagnostic tests. "Off the Gold Standard" If the goal of the study is to measure clinical outcomes rather than test accuracy, one can ethically enroll anyone who needs the index test.
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From page 64... ...
The alternative is to allocate patients at random to one of two putatively equivalent tests, perform the gold-standard test on aU patients, and then measure clinical outcomes. This approach allows one to compare accuracy and effect on shot-tern clinical outcomes, such as short-term morbidity and moronity, reduction in diagnostic uncertainty, and altered choice of therapy and other technologies.
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From page 65... ...
Ideally, a diagnostic test win always be compared to some other memos for obtaining information, such as the patient's history and physical examination or another diagnostic test. First the effects of two or more tests on clinical outcomes can be compared.
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From page 66... ...
All the Data that Are Neededfor Clinical Decision Making Should Be Collected Past studies have measured the accuracy of a test, but they have not collected all the data required to help physicians make decisions conceming individual patients. For instance, sequences of tests are not reported, although physicians must often choose between doing such a sequence or doing one test.
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From page 67... ...
To provide the data needed for decision making, studies of diagnostic tests should: Develop clinical prediction rules for estimating pretest probability. Clinical prediction rules estimate the probability of disease from the history and physical examination and other data (see Chapter 2~.
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From page 68... ...
If the range of treatment thresholds is relatively narrow, one can make general recommendations for using diagnostic tests. Bias in Patient Selection Should Be Avoicled In past studies of diagnostic tests, the study population has differed significantly from the patients who undergo the test in the usual course of medical care.
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From page 69... ...
Patients Should Be Observedfor Adverse Elects of the index Test Most studies of diagnostic tests have not included any clinical outcome measures other than diagnosis. ~ effects have seldom been assessed, other than to note direct complications (death and disability from the procedure itself)
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From page 70... ...
There Should Be Enough Patients to Report the Results in Clinically Useful Subgroups of Patients Typical studies of diagnostic tests enroll fewer than 100 patients, far too few to evaluate the perfonnance of a test in clinically important subsets of patients. One large clinical study has shown that Me accuracy of a diagnostic test vanes among clinically defined patient subgroups (Weiner et al.
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From page 71... ...
Coronary Artery Surgery Study (CASS) : A randomized trial of coronary artery bypass surgery: Survival data.
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From page 72... ...
Weiner, D.A., Ryan, T.~., McCabe, C.H., et al. Exercise stress testing: Correlations among history of angina, ST-segonent response, and prevalence of coronary-artery disease in He Coronary Artery Surgery Study (CASS)
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