**5.1 Measurement of thyrotropin-receptor antibodies in serum**

It is largely a matter of individual preference, whether serum thyrotropinreceptor antibodies should be measured in the differential diagnosis of GD, some argue that a test for the antibodies should be done routinely, and others that a diagnosis of GD can nearly always be inferred correctly on the basis of the clinical findings. The immunoglobulin-mediated inhibition of the binding of radiolabeled thyrotropin to thyrotropin receptors is most widely used assay for thyrotropin-receptor antibodies and is positive approximately in 80% of individuals suffering for Graves' hyperthyroidism [2]. Up to 99% sensitivity is shown by newer assays. Even though a positive result might specify the occurrence of either thyroid- stimulating antibodies or thyrotropin-receptor– blocking antibodies, it is rational to conclude that a positive test in the individual suffering from hyperthyroidism is owing to thyrotropin-receptor–stimulating antibodies. With time as the mechanism of the interactions of antibodies with the thyrotropin receptor improves, it would be possible to develop simple, precise immunoassays for thyroid-stimulating antibodies for routine use. The antibodies identified by bioassays that measure the synthesis of cAMP in retort to the stimulation of thyrotropin receptors are only thyroid-stimulating antibodies — for instance, in cells transfected with thyrotropin receptor— but such assays are relatively expensive and not widely available [71].
