Low serum thyrotropin is associated with high plasma fibrinogen

Background: Elevated plasma fibrinogen levels are associated with an increased risk of cardiovascular events. Decreased serum TSH predicts vascular mortality, which hypothetically could be explained in part by alterations in the blood coagulation system. Objective: The objective of this study was to investigate the association between thyroid function and plasma fibrinogen levels in a general population. Design: The population-based Study of Health in Pomerania was performed in a previously iodine-deficient area in Germany, including 4310 subjects, aged 20-79 yr. Data for 3804 individuals without thyroid disease were analyzed. Analysis revealed an association between thyroid function status and plasma fibrinogen concentration. Results: Elevated fibrinogen levels (> 3.25 g/liter) were observed in 14 subjects with increased serum TSH levels (32.6%), 973 euthyroid subjects (28.9%), 158 subjects with decreased serum TSH levels (40.7%), and six individuals with overt hyperthyroidism (54.4%). Logistic regression analysis revealed decreased serum TSH as an independent risk factor for elevated fibrinogen levels (odds ratio, 1.42; 95% confidence interval, 1.12-1.80). Conclusions: Thyroid function is associated with plasma fibrinogen. Decreased serum TSH is an independent risk factor for elevated plasma fibrinogen levels as a possible explanation for the high cardiovascular mortality among affected subjects.