MedWire News: Older age and greater body mass index (BMI) predict the activity of blood clotting factors (F)VIII, FIX, and FXI, while oral contraceptive use predicts FIX, FXI, and FXII activity, report German researchers.

In their study of 499 blood donors (69% men) and 286 patients with venous thromboembolism (VTE, 40% men), Beate Luxembourg (University Hospital Frankfurt) and team investigated the impact of age, gender, BMI, and oral contraceptive use on the activities of FVIII, FIX, FXI, and FXII, and their impact on the cutoff definition of elevated clotting factors.

The researchers found that age, BMI, and oral contraceptive use were significant independent predictors of FIX and FXI activity. FVIII was determined by age and BMI whereas FXII was only influenced by oral contraceptive use. Gender did not influence any of the clotting factors.

The influence of age, BMI, and oral contraceptive use considerably changed the percentiles of clotting factor activities, which are often used to determine cut-off points for elevated clotting factor levels as a risk factor for VTE. For example, the 90th percentile for FVIII activity varied from 141% to 177% depending on the characteristics of the control population.

After adjustment for age, gender, BMI, and oral contraceptive use, elevation of FVIII, FIX, FXI, and FXII conferred a 10.3-, 6.1-, 3.3- and 2.9-fold increased risk for VTE, respectively, compared with the reference group for each clotting factor.

“Our study confirms the increased risk associated with elevated clotting factor activities of FVIII, FIX, and FXI and shows for the first time an increased risk of VTE associated with high factor XII activities,” remark Luxembourg and co-authors in the journal Blood, Coagulation and Fibrinolysis.

They conclude that their data “show that recruitment of different control populations can influence the number of patients classified as being at increased risk for VTE because of elevated clotting factor activities.”

Furthermore, since oral contraceptive use had the greatest impact on the threshold for elevated factor VIII activities and was significantly less common in women who experienced VTE (1.2% of female patients in this study) than in those who did not, users of the pill should be excluded from populations recruited for cutoff definitions of elevated clotting factors, say the researchers.

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