Background: A high plasma level of factor VIII is a risk factor for venous
thromboembolism. We evaluated the risk of a recurrence of thrombosis after
an initial episode of spontaneous venous thromboembolism among patients wit
h high plasma levels of factor VIII.
Methods: We studied 360 patients for an average follow-up period of 30 mont
hs after a first episode of venous thromboembolism and discontinuation of o
ral anticoagulants. Patients who had recurrent or secondary venous thromboe
mbolism, a congenital deficiency of an anticoagulant, the lupus anticoagula
nt, hyperhomocysteinemia, cancer, or a requirement for long-term treatment
with antithrombotic drugs or who were pregnant were excluded. The end point
was objectively documented, symptomatic recurrent venous thromboembolism.
Results: Recurrent venous thromboembolism developed in 38 of the 360 patien
ts (10.6 percent). Patients with recurrence had higher mean (+/-SD) plasma
levels of factor VIII than those without recurrence (182+/-66 vs. 157+/-54
IU per deciliter, P=0.009). The relative risk of recurrent venous thrombosi
s was 1.08 (95 percent confidence interval, 1.04 to 1.12; P<0.001) for each
increase of 10 IU per deciliter in the plasma level of factor VIII. Among
patients with a factor VIII level above the 90th percentile of the values i
n the study population, the likelihood of recurrence at two years was 37 pe
rcent, as compared with a 5 percent likelihood among patients with lower le
vels (P<0.001). Among patients with plasma factor VIII levels above the 90t
h percentile, as compared with those with lower levels, the overall relativ
e risk of recurrence was 6.7 (95 percent confidence interval, 3.0 to 14.8)
after adjustment for age, sex, the presence or absence of factor V Leiden o
r the G20210A prothrombin mutation, and the duration of oral anticoagulatio
n.
Conclusions: Patients with a high plasma level of factor VIII have an incre
ased risk of recurrent venous thromboembolism. (N Engl J Med 2000;343:457-6
2.) (C)2000, Massachusetts Medical Society.