Lisette van Dam

Chapter 4 62 patients with a history of DVT. An abnormal D-dimer test was defined as abnormal according to the assay dependent threshold, which differed between the different assays used in the study. We considered different classifications of CUS results: normal/abnormal and positive/negative/inconclusive, reflecting clinical practice where the presence of a reference CUS is varied. A normal CUS was defined as full compressibility along the venous system. An abnormal CUS was defined as one or more non-compressible venous segments. A positive CUS was defined as a new non-compressible segment or a ≥ 2-4 mm increase in vein diameter of a previously non-compressible venous segment when compared to a prior reference CUS of the leg. 2,13 A negative CUS was defined as the absence of any non-compressible segments or the absence of a new non-compressible segment in comparison with a prior reference CUS and a < 2 mm increase in vein diameter of a previous non-compressible venous segment. An inconclusive CUS was defined as a non-compressible vein segment in the absence of a prior reference CUS for comparison. A MRDTI positive for acute recurrent DVT was defined as a high signal intensity in the location of a deep venous segment against the suppressed background greater than that observed in the contiguous segments or corresponding ipsilateral vein. Pulmonary embolism was considered to be present if computed tomography pulmonary angiography showed at least one filling defect in the pulmonary artery tree and if pulmonary embolismwas judged to be a probable cause of unexplained death unless proven otherwise by autopsy. Statistical analysis Baseline characteristics are described as mean with standard deviation (SD) or median with interquartile range (IQR). The primary outcome was calculated with corresponding exact 95% confidence interval (95% CI). Also, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) with corresponding 95% CI of a combination of an unlikely CDR and a normal D-dimer test were calculated. The reference standard for a correct negative ruling by the CDR and the D-dimer test was a negative MRDTI for DVT at baseline and an uneventful 3-month follow-up period. We defined the sensitivity to be adequate if its point estimate would exceed 96%, which was the upper limit of the 95% CI of the sensitivity of D-dimer testing for recurrent DVT in a large multicenter management trial. 14