Blood Disorders Excessive Factor Viii
Background: Elevations of coagulation factor VIII have recently been described in significant numbers of patients with venous thromboembolism (VTE) previously thought to have had an "idiopathic" event. Three patients from a family practice are presented with recurrent VTE and increased factor VIII levels.
Method: The case histories and results of laboratory tests were reviewed.
Results: The 3 patients had no other clear coagulopathy. In 2 of the 3, the increase was confirmed with a second reading.
Conclusions: Factor VIII assay should be considered in the work-up of idiopathic, recurrent VTE. Long-term anticoagulation may be appropriate in this setting.
Venous thromboembolism (VTE) is seen frequently in primary care. With the advent of sophisticated laboratory testing, at least half of previously idiopathic cases can be found to have a coagulation disorder. Although the heritable factor V Leiden mutation has been believed to be the most common of these (5% of the white population is heterozygous for the disorder), increased activity of factor VIII has recently emerged as a relatively common identifiable cause of hypercoagulability. In 1995, Koster et al studied 301 VTE patients without cancer and matched control subjects and found a dose-response relationship between factor VIII concentration and risk of thrombosis; subjects with factor VIII activity above 150% (150 IU/dL) represented 25% of the sample and had an adjusted odds ratio for VTE of 4.8. Kraaijenhagen et al found a 33% prevalence of factor VIII activity above 175% (the 90th percentile) in recurrent VTE cases, and concluded that such elevated plasma levels were a significant, prevalent, independent, and dose-related risk factor. Kyrle et al followed patients with a first episode of VTE after anticoagulants had been discontinued and found patients above the 90th percentile for plasma factor VIII levels had a 6.7-fold relative risk of recurrence compared with those with lower levels. Elevated factor VIII levels have been found to persist over time[4,6] and to be independent of the acute phase response.[6-8] (The studies above nevertheless remeasured factor VIII several months after the VTE event.)