Fibrinogen and D-dimer levels in autoimmune subclinical and overt hypothyroidism and effects of levothyroxine treatment.

Background. Hypothyroid patients may have several haemostatic abnormalities such as modification of the coagulation proteins and a bleeding tendency and conflicting data have been reported in this regard. Objectives. Aim of this study was to evaluate the alterations of fibrinogen and D-Dimer (D-D) in patients with subclinical hypothyroidism (SH) and in those with overt hypothyroidism (OH) before and after levothyroxine (L-T4) treatment, and to compare them with those of euthyroid controls. Patients and methods. The study prospectively included 17 OH patients (TSH >15 mU/l), 40 SH patients (TSH 3-15 mU/l) and 28 sex- and age-matched healthy controls. All hypothyroid patients had chronic Hashimoto’s thyroiditis. All patients were questioned about their current treatment, medical history and smoking habits. Their fibrinogen and D-D levels were evaluated before L-T4 treatment and after 3-6 months, in euthyroid state. Results. No difference in mean fibrinogen levels was observed in OH and SH patients compared with the healthy controls. Mean D-D levels were found to be significantly higher in SH patients (207.4187.6) than in controls (146.673.2; p = 0.01), but not in OH patients. It is worth noting that fibrinogen levels showed a significant increase when the euthyroid state was restored in OH patients (25020.6 vs 33970.7 ; p<0.005). Moreover, treatment did not affect D-D levels in SH and OH patients. Conclusions. These data suggest that both autoimmunity and thyroid failure, may concur in the modulation of fibrinogen in Hashimoto’s hypothyroidism. Higher fibrinogen levels due to chronic inflammation of autoimmune disease observed in OH only on L-T4 treatment could be the consequence of reduced liver synthesis in the hypothyroid state. The D-D increase in SH may be due to a chronic inflammation of Hashimoto’s thyroiditis. Whether and to what extent these subtle alterations of haemostatic parameters in autoimmune hypothyroidism are clinically relevant remains to be elucidated.