Unusual venous thrombosis

In a CMAJ practice article, Schattner1 provides guidance regarding when to test for thrombophilia and when to screen for occult cancer in patients with unprovoked venous thromboembolism (VTE). This issue is important, because unprovoked VTE is common (about 20 000 cases a year in Canada),2 and indiscriminate thrombophilia testing and extensive cancer screening occur frequently in clinical practice. We wish to emphasize two points. First, thrombophilia testing should be avoided because it does not affect clinical management in most patients.3^,4 Even if a thrombophilic abnormality is found, such as the factor V Leiden or prothrombin mutation, its presence does not affect risk for recurrent VTE and, therefore, does not affect decisions about continuing or stopping anticoagulant therapy. Exceptions to this premise occur; the antiphospholipid antibody syndrome or protein S or C deficiency will warrant long-term anticoagulation, but such cases are rare (< 5%). Overall, testing for thrombophilia rarely affects patient management, often yields false positive results and may adversely influence insurability of patients. We urge clinicians to consult colleagues with expertise in thrombosis before testing for thrombophilia.

Second, although screening for cancer (i.e., abdominopelvic CT, colonoscopy) may increase the number of cancers detected, it does not appear to improve cancer-related mortality, morbidity or quality of life.4 Moreover, such screening may incur procedure-related complications and psychological burden from false positive results.5 Ongoing randomized trials are assessing the risks and benefits of comprehensive screening for cancer in unprovoked VTE (NCT00773448, NCT01107327). In the meantime, we suggest age- and sex-appropriate screening for cancer, with additional testing only if patients have symptoms that are suspicious for malignant disease.