Background: During the last 15 years, several risk markers for atherosclerosis, such as fibrinogen and D-dimer, have been identified. The role of elevated fibrinogen levels as an independent risk factor for coronary, cerebral, and peripheral vascular disease is well established on the basis of clinical and epidemiological studies. Increased D-dimer levels are associated with increased risk of future myocardial infarction, stroke, and peripheral vascular disease. The aim of this study was to evaluate the alterations in fibrinogen and D-dimer, which indicates overall thrombotic activity, in subjects with subclinical hyperthyroidism.
Material/Methods: Thirty-six subclinical hyperthyroidic subjects and 36 euthyroidic control subjects matched for age, gender, and body mass index were selected. The levels of plasma fibrinogen and D-dimer in all subjects were measured.
Results: The level of fibrinogen was significantly higher in the subclinical hyperthyroidic group than in the euthyroidic group (296.9±74.3 mg/dl vs. 255.0±41.7 mg/dl, p<0.001). The level of D-dimer was significantly higher in the subclinical hyperthyroidic group than in the euthyroidic group (261.9±47.8 mg/dl vs. 216.4±32.1 mg/dl, p<0.000).
Conclusions: The results suggest that subjects with subclinical hyperthyroidism present a relatively hypercoagulable state. This state could contribute to increased thromboembolic risk in subclinical hyperthyroidism.

Keywords: Atherosclerosis - etiology, Case-Control Studies, Fibrin Fibrinogen Degradation Products - metabolism, Fibrinogen - metabolism, Hyperthyroidism - complications, Risk Factors, Thromboembolism - etiology