Some common thyroid diseases occur when the immune system breaks down and produces antibodies against its own thyroid gland. Antithyroglobulin antibodies (AcTG, anti-TG) and antimicrosomal antibodies (anti-TPO) are the most frequently implicated autoantibodies.
Levels of antithyroglobulin antibodies vary in the same way as levels of antimicrosomal antibodies (see that heading), and in most cases, only the measurement of antimicrosomal antibodies is clinically justified.
Thyroglobulin is the most abundant component of thyroid cells. The measurement of even very low levels of thyroglobulin can detect the presence of residual thyroid tissue after thyroid cancer treatment (surgery or radiation). In such cases, the antithyroglobulin antibodies present in the patient’s blood are likely to interfere with the measurement of thyroglobulin levels. Antibody levels cannot be used to determine how extensive the interference was, nor whether it was positive or negative. They can only be used to alert the treating physician of the possibility of such interference.