Relationship of thyroid states and serum thrombomodulin (TM) levels in patients with Graves' disease: TM, a possible new marker of the peripheral activity of thyroid hormones.

Thrombomodulin (TM) is a thrombin receptor glycoprotein that functions as an anticoagulant on the surface of endothelial cells. Serum TM is regarded as a new marker of generalized endothelial cell damage. Serum TM concentrations were measured in 75 patients with Graves' disease and 75 age- and sex-matched healthy subjects. Serum TM levels in patients in the hyperthyroid state were significantly increased, while those in patients in the hypothyroid state due to treatment were significantly decreased compared with levels in control subjects. All patients with untreated Graves' disease had markedly elevated TM levels. Serum TM levels correlated closely with thyroid hormone concentration (TM vs. free T4, r = 0.858; P = 0.001). Serial measurement of individual patients revealed that serum TM levels paralleled thyroid hormone concentration, reaching normal control values upon attainment of euthyroidism. On the other hand, there was no significant correlation between serum TM concentration and titer of antithyroglobulin antibodies, titer of antimicrosomal antibodies, serum thyroglobulin level, or goiter size, and serum TM was not directly influenced by TSH receptor antibodies or resting pulse rates. The close correlation between serum TM and thyroid hormone concentration suggests that thyroid hormones might influence the synthesis or metabolism of TM on the surface of endothelial cells in patients with Graves' disease.