Lisette van Dam

Chapter 3 40 and was set at 1.7% versus 1.1% for non-intracranial major bleeding, 0.25% versus 0.09% for intracranial bleeding and 8.4% versus 6.6% for CRNM bleeding. 25 For this analysis, initial diagnostic costs were defined as diagnostic costs including ED admission, and both laboratory and imaging costs for the first hospital presentation. Return diagnostic costs included the costs for ED readmission, and both laboratory and imaging costs for patients returning for repeated diagnostic imaging after a missed DVT diagnosis. The treatment costs were defined as anticoagulant medication costs, management costs and costs for bleeding complications for all patients with recurrent DVT. The overtreatment costs included the anticoagulant medication costs, management costs and costs for bleeding complications for patients who were falsely diagnosed with recurrent DVT. Decision analytic model From patient-level data of the Theia study, the prevalence of recurrent ipsilateral DVT was calculated as was the diagnostic accuracy of each test, conditional to the outcome of preceding tests and disease prevalence ( Figure 1 ). From these, the true-positive, false-negative, true-negative, and false-positive rates of each of the 10 diagnostic scenarios were estimated. False negative diagnoses (also referred to as misdiagnosis in this analysis) were defined as 1) patients in whom recurrent DVT was excluded based on an unlikely CDR in combination with a normal D-dimer or based on a negative CUS but with a positive MRDTI for recurrent DVT or 2) patients in whom recurrent DVT was excluded based on a negative MRDTI but with recurrent VTE during 3 months of follow-up. False positive diagnoses were defined as patients with a positive or inconclusive CUS, but negative MRDTI for recurrent DVT. For reference, we also assessed scenarios that treat all patients, treat no patients and treat only those patients with a likely CDR and/or abnormal D-dimer (i.e. scenarios without imaging tests). These reference scenarios are hypothetical and do not serve as a realistic or ethically defendable scenarios for clinical practice. For each scenario, costs of diagnostic tests were counted for the number of patients undergoing the tests. For each true-negative outcome, only the initial diagnostic costs were counted ( Figure 2 ). For each true-positive and false-positive outcome additional treatment and overtreatment costs, respectively were counted. For false-negative outcomes, we conservatively made the following three assumptions. First, we assumed that all patients with a false-negative diagnosis would return to the ED for repeated diagnostic testing. Second, the costs of the