[Blood tests and imaging in thyroid pathology]

Circulating analytes used in the exploration of thyroid function are TSH and free thyroid hormones (FT4 and FT3). TSH is used as first line analysis in diagnosis because a normal value excludes almost always a thyroid dysfunction. However in the follow up of a treatment for hypo- or hyperthyroidism, free hormones are to be determined since TSH reaction is delayed and does not reflect precisely the restoration of euthyroidism. The measurement of anti-thyroperoxidase antibodies (anti-TPO) will show the presence of an autoimmune thyroiditis and that of thyroid stimulating antibodies (TSI) will establish the diagnosis of Graves' disease. The measurement of circulating thyroglobulin has no place in the diagnostic of thyroid dysfunction nor in the evaluation of a goitre but it is now the golden standard in the follow up of patients with a differentiated thyroid cancer after surgery and radioiodine ablation in patients without antithyroglobulin antibodies. Echography is the first line examination to evaluate thyroid morphology. It shows tiny thyroid nodules and gives precious informations on their structure, as well as paremchymatous diffuse abnormalities associated with thyroiditis. Thyroid scintigraphy with 99mTc allows establishing the functional characteristics of thyroid nodules (warm or cold) and to precise the origin of a thyrotoxicosis (autonomous toxic nodule vs Graves-Basedow, sub acute or silent thyroiditis). Whole body scintigraphy is mandatory after radioiodine treatment with 131I in order to visualize possible metastasis and establish their avidity for iodine.