Objectives & Background Current assessment protocols for suspected acute venous thromboembolism (VTE) have low specificity. As a result, many patients without disease receive high dose anticoagulation or undergo hospital admission for short periods pending definitive investigation. Elderly patients are particularly at risk. It has been suggested that increasing the threshold for a positive d-dimer test in patients over 50 years old may lead to significantly increased specificity of the test, without decreasing sensitivity. We sought to identify the clinical and cost impact of a variable ‘age adjusted' threshold in the Manchester area, to externally validate these findings⇓.
Methods A multicentre 6 month retrospective cohort study. Patients undergoing invasive investigation for exclusion of VTE were identified in several centres undertaking ambulatory management. All patients were identified as disease positive or negative via gold standard imaging. Serum d-dimer measurements collected on initial assessment were recorded. Age adjusted cut offs were calculated retrospectively by formula in line with recent evidence (age*10).
Diagnostic test characteristics were calculated along with proportional reductions in imaging, therapeutic exposure and baseline estimates of cost.
Results During the study period, 497 patients over 50 years of age were identified who were referred for definitive investigation to exclude VTE. Mean age was 74. Incidence of VTE was 16.3%. Use of an age adjusted cut point for d-dimer measurement would have resulted in withheld imaging/treatment in 138 patients (35.8%). Of these patients, 2 were false negative results – an 85 year old with a 5 week history of back pain eventually treated as a pulmonary embolus after high probability v/q scan, and an isolated distal deep vein thrombosis in a 72 year old. Test characteristics are displayed in Table 1. The strategy would have saved 128 doppler scans, 10 V/Q scans and 2 CTPA scans, in addition to 652 days of LMWH administration over the 6 month period, at a cost estimate of £11,620.56.
Conclusion Retrospective application of an age adjusted d-dimer cut point for exclusion of VTE in ths cohort significantly increased specificity with limited impact on sensitivity. Caveats include those patients with longstanding symptoms and those with isolated distal deep vein thrombosis. UK centres should consider further local validation and trial adoption.
- emergency departments
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