[Strategy for laboratory tests of thyroid function (author's transl)].

Clinical findings suggesting hyperthyroidism should be confirmed by the following basic tests of thyroid function: serum T3 and T4, and iFT4. In the case where there is contradiction between the T3 and T4 values, hyperthyroidism may be confirm by the absence of effect of TRH on serum TSH level. Clinical findings suggesting hypothyroidism should be confirmed by the following basic tests: serum T3 and T4, iFT4, and serum TSH which also will be greatly helpful in the differentiation of primary or secundary hypothyroidism. When there is an absence of parallelism between total and free T3 and T4 determinations, it is necessary to look for a possible abnormality in the binding protein. In vivo explorations (radio-iodine uptake, scintigraphy) and other assays should be proposed in view of clinical findings but should not be systematically prescribed.