TSBAb (TSH-stimulation blocking antibody) and TSAb (thyroid stimulating antibody) in TSBAb-positive patients with hypothyroidism and Graves' patients with hyperthyroidism

There are two types of TSH receptor antibodies (TRAb); thyroid stimulating antibody (TSAb) and TSH-stimulation blocking antibody (TSBAb). TSAb causes Craves' hyperthyroidism. TSBAb causes hypothyroidism. Both TSAb and TSBAb block TSH-binding to thyroid cells as TSH receptor antibodies (TRAb). TSBAb-positive patients with hypothyroidism and Craves' patients with hyperthyroidism may have both TSBAb and TSAb. We studied TSBAb and TSAb in 43 TSBAb-positive patients with hypothyroidism and in 55 untreated Graves' patients with hyperthyroidism, TSBAb-activities were expressed as percentage inhibition of bovine (b) TSH-stimulated cAMP production by test IgG, Two formulas were used to calculate TSBAb-activities: TSBAb-A (%) = [1-(c-b)/(a-b)] x 100 and TSBAb-B (%)= [1-(c-d)/(a b)l x 100, where a: cAMP generated in the presence of normal IgG and bTSH, b: dAMP generated in the presence of normal IgG, c: cAMP generated in the presence of test IgG and bTSH, and d: cAMP generated in the presence of test IgG. TSAb (%) = [d/b] x 100. All of the 43 TSBAb-positive patients with hypothyroidism had strongly positive TSBAb-A and -B. Some of them had weakly positive TSAb (< 240%). All 55 untreated Craves' patients had positive TSAb (205-2509%), Some of them had both TSAb and TSBAb, TSBAb-positive patients with hypothyroidism had a limited distribution of TSBAb- and TSAb-activities wTSBAb-A+75-+103%,TSBAb-B+87-+106%,TSAb92-240%), but Graves' patients with hyperthyroidsim had a wide distribution of TSAb- and TSBAb-activities (TSAb 205-2509%. TSBAb-A-158-+43%, TSBAb-B-14-+164%), TSBAb-A ignores TSAb activity in serum, and might give low TSBAb activity. However, TSBAb-A clearly differentiates TSBAb-positive patients with hypothyroidism from Graves' patients with hyperthyroidism; thus, we favor TSBAb-A over TSBAb-B. Some of TSBAb-positive patients with hypothyroidism and Graves' patients with hyperthyroidism have both TSBAb and TSAb.