My patient has normal thyroid hormone concentrations, but has an elevated thyroglobulin autoantibody result. What does this mean?
This most likely reflects the presence of subclinical thyroiditis (but very rarely might indicate thyroid neoplasia in an older dog). In these cases, there is evidence of pathology within the thyroid glands, but not to the extent that it is interfering with thyroid function. Histologically, there are often small foci of lymphocytic inflammation scattered through otherwise healthy appearing thyroid tissue. We estimate that it takes >60% destruction of thyroid tissues by the inflammatory process before we see changes in laboratory measures of thyroid function. It appears that the progression to overt hypothyroidism in these cases is often very slow and that, indeed, some may never have progression of pathology but remain euthyroid for many years, if not for their whole lifetime.
