Previous studies on the prevalence of biological abnormalities causing
venous thrombosis and the clinical characteristics of thrombotic patients are conflicting. We conducted a prospective study on 2.132 consecutive evaluable patients with
venous thromboembolism to determine the prevalence of biological causes.
Antithrombin,
protein C,
protein S,
plasminogen and
heparin cofactor-II deficiencies, dysfibrinogenemia,
lupus anticoagulant and
antiphospholipid antibodies were investigated. The risk of any of these alterations in patients with familial, recurrent, spontaneous or juvenile
venous thrombosis was assessed. The overall prevalence of
protein deficiencies was 12.85% (274/2,132) and
antiphospholipid antibodies were found in 4.08% (87/2,132). Ten patients (0.47%) had
antithrombin deficiency, 68 (3.19%)
protein C deficiency, 155 (7.27%)
protein S deficiency, 16 (0.75%)
plasminogen deficiency, 8 (0.38%)
heparin cofactor-II deficiency and 1 had dysfibrinogenemia. Combined deficiencies were found in 16 cases (0.75%). A
protein deficiency was found in 69 of 303 (22.8%) patients with a family history of
thrombosis and in 205/1,829 (11.2%) without a history (crude odds ratio 2.34, 95% CI 1.72-3.17); in 119/665 (17.9%) patients with
thrombosis before the age of 45 and 153/1,425 (10.7%) after the age of 45 (crude odds ratio 1.81, 95% CI 1.40-2.35); in 103/616 (16.7%) with spontaneous
thrombosis and in 171/1,516 (11.3%) with secondary
thrombosis (crude odds ratio 1.58, 95% CI 1.21-2.06); in 68/358 (19.0%) with recurrent
thrombosis and in 206/1,774 (11.6%) with a single episode (crude odds ratio 1.78, 95% CI 1.32-2.41). Patients with combined clinical factors had a higher risk of carrying some deficiency. Biological causes of
venous thrombosis can be identified in 16.93% of unselected patients. Family history of
thrombosis, juvenile, spontaneous and recurrent
thrombosis are the main clinical factors which enhance the risk of a deficiency. Laboratory evaluation of thrombotic patients is advisable, especially if some of these clinical factors are present.