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D-dimer testing to select patients with a first unprovoked venous thromboembolism who can stop anticoagulant therapy: a cohort study.

BACKGROUND
Normal D-dimer levels after withdrawal of anticoagulant therapy are associated with a reduced risk for recurrence in patients with unprovoked venous thromboembolism (VTE) and may justify stopping treatment.


OBJECTIVE
To determine whether patients with a first unprovoked VTE and negative D-dimer test result who stop anticoagulant therapy have a low risk for recurrence.


DESIGN
Prospective management study with blinded outcome assessment. (ClinicalTrials.gov: NCT00720915).


SETTING
13 university-affiliated clinical centers.


PATIENTS
410 adults aged 75 years or younger with a first unprovoked proximal deep venous thrombosis or pulmonary embolism who had completed 3 to 7 months of anticoagulant therapy.


INTERVENTION
Anticoagulant therapy was stopped if D-dimer test results were negative and was not restarted if results were still negative after 1 month.


MEASUREMENTS
Recurrent VTE during an average follow-up of 2.2 years.


RESULTS
In 319 patients (78%) who had 2 negative D-dimer results and did not restart anticoagulant therapy, rates of recurrent VTE were 6.7% (95% CI, 4.8% to 9.0%) per patient-year overall (42 of 319), 9.7% (CI, 6.7% to 13.7%) per patient-year in men (33 of 180), 5.4% (CI, 2.5% to 10.2%) per patient-year in women with VTE not associated with estrogen therapy (9 of 81), and 0.0% (CI, 0.0% to 3.0%) per patient-year in women with VTE associated with estrogen therapy (0 of 58) (P = 0.001 for the 3-group comparison).


LIMITATIONS
Imprecision in female subgroups. Results may not be generalizable to different D-dimer assays from the one used in the study.


CONCLUSION
The risk for recurrence in patients with a first unprovoked VTE who have negative D-dimer results is not low enough to justify stopping anticoagulant therapy in men but may be low enough to justify stopping therapy in women.


PRIMARY FUNDING SOURCE
Canadian Institutes of Health Research.