Consistency and variability in the character of thyrotrophin receptor antibodies in Graves' disease

At diagnosis there was no correlation between the uptake of pertechnetate by the thyroid and thyrotrophin receptor antibodies (TRAb) measured as TSH binding inhibitory immunoglobulins in a series of 27 patients with Graves' disease. TRAb were detectable initially in 19 patients, in 11 of these there was a significant positive correlation (P less than 0.05) between serial measurements of pertechnetate uptake and TRAb made during 2 years following diagnosis. In five patients pertechnetate uptake fell with time whilst TRAb levels were maintained or fluctuated. In the remaining three of the 19 patients both measurements were low and did not change during treatment. We conclude that TRAb in any individual patient are a mixture of immunoglobulins of variable effectiveness as thyroid stimulators. In a majority of patients the composition of this mixture remains constant during the course of the illness and the clinical state reflects the levels of TRAb in the blood. In a minority, however, the character of these antibodies may alter with time or there is a change in the responsiveness of the thyroid gland. The general lack of correlation between measurements of thyroid stimulating activity and TSH binding inhibitory immunoglobulins in groups of patients is due to differences between patients in the composition of TRAb.