Haemostatic profile in hypothyroidism as potential risk factor for vascular or thrombotic disease

Background The influence of thyroid failure on haemostasis is controversial , both hypocoagulable and hypercoagulable states have been reported. Since both subclinical and overt hypothyroidism have been associated with atheros clerosis, a hypercoagulable state in addition might represent a risk factor for thromboembolic disease. Design We investigated various haemostatic variables in 42 women with subcl inical hypothyroidism and compared them to 66 euthyroid controls. Prothromb in time, activated partial thromboplastin time, fibrinogen, factor VII acti vity (FVII:C), factor VII antigen (FVII:Ag), factor VIII activity, von Will ebrand factor (vWF), antithrombin III, heparin cofactor II, protein C, prot ein S, plasminogen, antiplasmin, plasminogen activator inhibitor and tissue plasminogen activator, as well as common lipid variables, were measured. Results Factor VII:C (P < 0.02) and the ratio FVII:C/FVII:Ag (P < 0.01) wer e significantly increased in subclinical hypothyroid patients compared to t he control group. Both parameters remained higher in hypothyroid patients a fter exclusion of 18 women on oestrogen replacement therapy. No differences were found between the groups with respect to vWF or the other haemostatic and lipid variables tested. Conclusion Patients with subclinical hypothyroidism had significantly highe r levels of FVII:C. The greater increase in FVII:C compared to that of FVII :Ag, as shown by the increase in their ratio, might reflect the presence of activated FVIIa. This might mean a hypercoagulable state, which could cont ribute to the increased prevalence of coronary heart disease reported in su ch patients. A hypercoagulable state might be another argument in favour of thyroxine replacement treatment in subclinical hypothyroidism, especially in patients with additional risk factors for vascular disease.