evidence exists for the reasonableness and necessity of diagnostic tests has two main components. First, the evidence must be adequate to determine whether the test provides more accurate diagnostic information than existing tests. Second, if the test provides more accuracy, the evidence must be adequate to determine how the changed accuracy affects health outcomes. For example, does it change patient management, and do those changes in patient management actually improve outcomes?

At the request of the Centers for Medicare and Medicaid Services (CMS), experts at Duke University conducted an evidence review on the use of positron emission tomography (PET) in scanning for Alzheimer’s disease. The review concluded that there was adequate evidence to conclude that PET scanning has better sensitivity and specificity than clinical evaluation by an expert neurologist. The experts also constructed a decision model which determined that because available treatments had very limited efficacy and were relatively safe (i.e., treatments for dementia are basically nontoxic and not very effective), the new diagnostic information available from the PET scans had essentially no effect on patient management—that is, it would not change patient outcomes. Furthermore, the small false-negative rate of PET scans might lead to withholding treatment and might lead to worse outcomes than empirically treating anyone with a clinical diagnosis of dementia.

In light of this, Medicare policy is to not cover PET scans for Alzheimer’s disease except in the context of a prospective clinical trial that would evaluate whether the information from PET scans changed patient management in other important ways. Medicare agreed to cover tests in the context of such a study, and a proposal for such a study was developed by scientists at the University of California at Los Angeles and submitted to the National Institutes of Health, but it was never funded. So the practical effect of this policy is that Medicare does not pay for any PET scanning for Alzheimer’s disease.

What do other payers need in order to determine whether to pay for a diagnostic test? One major private payer’s policy on the clinical utility of ambulatory electocardiograms (ECG) is that ambulatory ECG is considered experimental and investigational because of the lack of peer-reviewed published reports of prospective clinical trials on the effectiveness of the distinct features of ECG in improving clinical outcomes over standard cardiac event-monitoring services. What this payer is saying, in other words, is that in order to qualify the service for reimbursement one would need to conduct a prospective study of ambulatory ECG versus Holter monitoring, and the results would need to demonstrate that some important clinical outcome was changed as a result of the use of ambulatory ECG.

Such a study has never been done, Tunis said, and it is unlikely that any company manufacturing ambulatory ECGs will ever conduct such a study.

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