Background: Diagnostic tests, particularly diagnostic imaging modalities such as computed tomography (CT) and positron emission tomography (PET), have the potential to make important contributions to improved patient care and medical decision making. The expense of these tests is justified to the extent that they improve diagnostic and treatment decisions, and ultimately health outcomes. Clinical studies evaluating the accuracy of diagnostic tests and assessing their influence on decision making are essential to setting health policy and directing patient care. Purpose: We present the design and participant baseline characteristics of the Department of Veterans Affairs Cooperative Study 027 (Prospective Study of the Diagnostic Accuracy of 18F-Fluorodeoxyglucose (FDG) - Positron Emission Tomography (PET) Imaging in the Management of Patients with Solitary Pulmonary Nodules (SNAP). Methods: SNAP is a prospective, multi-site diagnostic trial to evaluate the efficacy of PET and CT for characterizing solitary pulmonary nodules. The study incorporated an assessment of the impact of these imaging modalities on clinical decision making. Results: Between January 1999 and June 2001, 10 SNAP sites enrolled 532 participants with a mean age of 66 years (SD ± 11.3), of whom 97.3% were male. A history of smoking was claimed by 93.6% of participants, with 45.7% of all participants smoking at time of enrollment. Those still smoking had an average exposure of 56.8 pack-years, while those who had quit smoking prior to enrollment had an exposure of 58.1 pack-years. Limitations: The study design reduced most common biases, but some degree of selection bias and verification bias remained. We sought to minimize verification bias by use of a dual reference standard. Conclusion: SNAP is a diagnostic test study that was designed to minimize bias and to assess a test's impact on clinical decision making, providing the kind of information most needed by clinicians and health policy makers.
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