Apparent different thrombotic tendency in patients with factor V Leiden and protein C deficiency due to selection of patients

Both activated protein C (APC) resistance and protein C deficiency are associated with an increased risk for venous thrombosis. To assess their tendencies to venous thrombosis, we compared the median age of first venous thromboembolism in patients with factor V Leiden or protein C deficiency, who were identified either within unselected consecutive cases with a first deep venous thrombosis derived from a population-based case-control study, or identified by selection of patients with a deep venous thrombosis, who were referred for thrombophilia work-up. The median age of onset for 92 unselected APC resistant cases was 43 years and for 13 unselected protein C-deficient cases 47 years. The median age at the first thrombotic event for 28 APC-resistant members of thrombophilia families was 29 years and for 50 protein C-deficient members of thrombophilia families 31.5 years. The median age of onset for all unselected patients (n = 105) was 45 years of age (range, 16 to 69 years) and the median age of onset for all selected patients from the thrombophilia families (n = 78) was 30.5 years (range, 16 to 67 years). These results show that within the case-control study and the family studies, the median age of onset is very similar in patients with APC resistance and patients with protein C deficiency. This suggests that APC resistance is not less severe with respect to risk of thrombosis than (heterozygous) protein C deficiency. In conclusion. the median age at which the first thrombosis occurs mainly depends on the way the patients are identified and not on the type of thrombophilia. (C) 1996 by The American Society of Hematology.