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Noninvasive diagnosis of deep vein thrombosis in postoperative patients
1McMaster University Clinic, Henderson General Hospital, Hamilton, Ontario, Canada.
Insights
Noninvasive tests for asymptomatic deep vein thrombosis (DVT) have limited accuracy. Abnormal results require venography confirmation, and routine surveillance does not improve outcomes in patients receiving prophylaxis.
Area of Science:
- Vascular Medicine
- Diagnostic Imaging
- Thrombosis Research
Background:
- Asymptomatic deep vein thrombosis (DVT) diagnosis is challenging due to distal vein involvement and smaller thrombi.
- Noninvasive testing for asymptomatic DVT has a positive predictive value of 80% or less, necessitating venography for confirmation.
Purpose of the Study:
- To evaluate the utility of asymptomatic DVT detection in postoperative patients for secondary prophylaxis.
- To assess the reliability of asymptomatic DVT as a surrogate for clinically significant venous thromboembolism (VTE) in prophylaxis trials.
Main Methods:
- Review of existing evidence on noninvasive testing accuracy for asymptomatic DVT.
- Analysis of clinical outcomes in patients undergoing routine surveillance for postoperative DVT.
- Evaluation of asymptomatic VTE as a surrogate endpoint in VTE prophylaxis studies.
Main Results:
- Routine surveillance for asymptomatic postoperative DVT does not improve clinical outcomes when appropriate VTE prophylaxis is administered.
- Asymptomatic VTE may not be a reliable surrogate for clinically important VTE, especially when comparing antithrombotic agents.
Conclusions:
- Noninvasive testing for asymptomatic DVT has limited accuracy and is unsuitable for routine surveillance or evaluating new prophylaxis methods in clinical trials.
- Abnormal noninvasive test results for asymptomatic DVT require venography confirmation.
Abstract:
The accuracy of noninvasive testing for the diagnosis of deep vein thrombosis (DVT) generally is less in asymptomatic patients than it is in those with symptoms suggestive of thrombosis. This is because asymptomatic DVT often is confined to the distal veins and, when it involves the proximal veins, the thrombi usually are smaller than in symptomatic patients with proximal thrombosis. Because the positive predictive value of noninvasive tests for asymptomatic DVT generally is 80% or less, abnormal results should be confirmed by venography. There are two main reasons why asymptomatic DVT is sought in the postoperative period: (1) to identify the need for full-dose anticoagulant therapy to prevent symptomatic episodes of venous thromboembolism (VTE), including fatal pulmonary embolism (this represents a form of secondary prophylaxis), and (2) to use this outcome as a surrogate for episodes of clinically important VTE in studies that are designed to evaluate methods of venous thrombosis prophylaxis. In relation to the first of these indications, evidence suggests that routine surveillance of high-risk patients to detect asymptomatic postoperative DVT does not result in improved clinical outcomes in patients who received appropriate VTE prophylaxis. In relation to the second indication, there is concern that asymptomatic VTE may not be a reliable surrogate for clinically important VTE, particularly if the effectiveness of different antithrombotic agents is being compared. Coupled with the comparatively low accuracy of noninvasive testing for asymptomatic DVT, this suggests that the results of such testing are unsuitable for the evaluation of new methods of prophylaxis in clinical trials.