Serum beta 2-microglobulin levels in thyroid diseases.

Serum beta 2-microglobulin was measured in 38 patients with thyroid diseases. Serum levels of beta 2-microglobulin were significantly increased in patients with untreated Graves' disease (median: 200 nmol l-1; P less than 0.0002), and in patients with untreated toxic adenomas (222 nmol l-1; P less than 0.0005) compared to 60 healthy control subjects (147 nmol l-1). Following antithyroid treatment of euthyroidism, serum beta 2-microglobulin decreased significantly in both Graves' disease (162 nmol l-1) and toxic adenomas (175 nmol l-1); values which were not significantly different from that of the control group. The level of serum beta 2-microglobulin in 12 patients with hypothyroidism was not different from that of the control group. However, in untreated hypothyroidism serum beta 2-microglobulin was positively correlated with serum thyroxine (T4) (rho = 0.69; P less than 0.05) and free thyroxine index (FT4I) (rho = 0.72; P less than 0.02). It is concluded that elevated levels of serum beta 2-microglobulin may reflect the increased metabolism in patients with thyrotoxicosis. Increased levels in active Graves' disease may also partly be caused by immunological activation.