D-dimer test in deep vein thrombosis - reply

Abstract

Dear Sir, We thank Dr Chow and colleagues for their thorough review (p.575, this issue) of our recent paper about the D-dimer test in deep vein thrombosis (DVT) [1]. It is true that a subsequent clinical evaluation of the patients' eventual outcome could be the gold standard, but as the use of a D-dimer test always takes place in an acute setting, it would not affect the choice of initial treatment of the patient. We are well aware of the study by Wells et al. [2] on the value of assessment of pretest probability of DVT. In this study, only three (0.6%) of 501 patients who were diagnosed as not having DVT had events during the 3-month follow-up. This indicates that a clinical follow-up would not add much to our study. The main purpose of this prospective study was to evaluate how the use of D-dimer assays compares with ultrasonography in confirmation or exclusion of DVT in the acute setting, reflecting a routine scenario to many clinicians. Introduction of a nonroutine venography or a 3-month follow-up as a gold standard, would not address this purpose appropriately. Venography is often referred to as the reference gold standard for the diagnosis of DVT, but because of its invasive nature and associated side-effects it has widely been replaced by compression ultrasonography [3]. In this study, we did not include phlebography as the gold standard. This is primarily based on results from a previous Danish study from The Department of Radiology, Aalborg Hospital, on the diagnostic performance of phlebography versus compression ultrasonography [4]. In this study, the positive and negative predictive value of compression ultrasonography was 100 and 85%, respectively. It is generally recommended that reasonable methodological standards are used in the documentation of diagnostic accuracy of clinical tests [5]. In this regard, the use of venography will only provide a theoretical evidence rather than an empirical evidence.