Clinical probability assessment and biochemical markers in the diagnosis of deep vein thrombosis

University dissertation from Lund university

Abstract: The combination of pre-test clinical probability assessment and D-dimer test is now widely applied in the diagnostic process of DVT. The general objective of the present investigation was to validate these results in a Swedish routine emergency setting were the prevalence of the disease is high and were the clinical probability assessment was handled by many junior physicians. Furthermore, our aims were to evaluate our D-dimer method and to make comparisons with other D-dimer methods as with a new marker of coagulation, the APC-PCI complex. In addition, a cost effectiveness analysis was made of this diagnostic strategy. Material and methods: 357 outpatients with clinical suspicion of DVT were included in the clinical management study. The diagnostic workup included estimation of pre-test probability, D-dimer determination, objective imaging as well as 3 month clinical follow up of negative patients (Paper I). 350 plasma samples from the management study was used for comparison between two well established D-dimer methods and the APC-PCI complex (Paper II) and 311 plasma samples for the evaluation of two new D-dimer methods (Paper III). Direct and indirect costs were calculated for the tested diagnostic strategy and for two hypothetical strategies. A decision analysis was performed (Paper IV). Results and conclusions: One out of 110 patients categorized as having a low clinical probability in combination with a negative D-dimer test was diagnosed with DVT during follow up. About 30% of the patients do not need further investigation for DVT. The APC-PCI complex perform inferior to the D-dimer methods for the exclusion of DVT but slightly superior when indicating its presence. The AxSYM® and Innovance™ D-dimer assays perform well and in good agreement with the two well established assays with NPV´s of > 98% in the low clinical probability estimate (CP). Objective imaging in all patients was the least cost effective (€581) strategy, D-dimer screening of all patients before CP (€421) and CP in combination with D-Dimer testing only in patients with low CP (€406). Conclusion: the investigated diagnostic strategy is safe, result in more convenient and cost-effective care for patients.

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