Home
About HEMEX
Educational Info
Test Menus
Client Services
Billing Services
Contacting HEMEX
Disclaimer / Privacy
FROM ANECDOTE TO REALITY
Factor VIII Activity and Thrombophilia (Clotting)
Risk
For many years it was recognized that Factor VIII activity values were elevated in many clinical
situations. This was thought to be related to an acute phase response reaction secondary to
inflammatory mediators such as cytokines. Given the important role of
factor VIII in the coagulation pathway, it was speculated that the high
levels of factor VIII sometimes in the 250-500% range could be consider
ed a risk. This was further supported by the finding that global tests
of coagulation function such as the APTT were shorter in patients with
high factor VIII.
Until recently, there were no studies in the literature that clearly showed an association between an increased risk of venous thrombophilia and elevated factor VIII values. In 1995 a Dutch group presented clear evidence that persistent factor VIII levels 150% were a valid risk factor
independent of acute phase reactant responses or related to von Willebrand factor (vWF) levels.
They also provided a risk assessment supporting an odds ratio of 4.8
for this factor VIII increase that took into account such variables as
blood groups and vWF.
Another study from England in May 1997, confirmed and strengthened the
initial data. The authors found that high factor VIII activity was a risk
factor for thrombosis. Unlike the original study, they confirmed that this
increase in plasma factor VIII activity represented a true increase in
protein levels by using the factor VIII antigen test, not a potential artifact
in quantitating factor VIII activity by clotting assay.
In a review of 260 patients with thrombosis, 25% of the patients had
a factor VIII activity >150%. When all other identifiable causes of thrombosis
were eliminated, 17% of these patients had an elevated factor VIII as the
only known risk factor.
These two studies strongly support the incorporation of testing for
factor VIII activity as part of the routine evaluation of thrombophilia
patients.
References:
1. Koster T, Blann AD, Rosendaal FR, Briet E et al, Role of Clotting Factor VIII in Effect of von Willebrand Factor on Occurrence of DVT. Lancet 1995; 345; 152-5
2. O'Donnell, Tuddenham Egd, Manning
R, et al, High prevalence of elevated factor VIII levels in patients referred
for thrombophilia screening: Role of increased synthesis and
relationship
to acute phase reaction. Thrombosis & Haemostasis. 1997: 77(5); 825-8.
3. Van der Meer FJM, Koster T, Vandenbroucke JP, et al The Leiden Thrombophilia Study (LETS). Thrombosis & Haemostasis. 1997: 78(1); 631-5.fac