The diagnosis of thyrotoxicosis.

Thyrotoxicosis is a clinical syndrome due to excessive amounts of thyroid hormone in the circulation and tissues. Graves' disease, goitre and exophthalmos, is the commonest variety, but in some parts of the world thyrotoxicosis supervenes on the background of a long standing nodular goitre. Other varieties such as ectopic TSH syndromes are very rare. The diagnostic sequence in practice starts with clinical suspicion and a decision can often be made on the symptoms and signs alone. It is, however, always advisable to confirm the presence or absence of thyrotoxicosis. There has been re-orientation in the simple test procedure used in this respect. Measurements such as serum TSH and serum TSH response to TRH and measurements of serum LATS levels are available only in a few centres and are not discussed in detail. Tests based on the carriage of thyroid hormones in the blood are preferable to radionuclide studies, particularly when the patient is thought to be euthyroid. We advise a serum PBI and serum total thyroxine estimation in all patients. If the data are abnormal we add a serum T3 resin estimation to check whether the values are due, for example, to iodine contamination or altered binding. We advise radionuclide studies in all doubtful cases and measurements such as the 4 hr or 24 hr I uptake and the 48 hr serum PBI are very helpful. A thyroid uptake suppression test may be required if there is still doubt. In general those patients going for thyroidectomy or I therapy should have a scan performed. With improved technology much safer radionuclides, such as I or Tc, may be usable when thyrotoxicosis is suspected in children or during pregnancy.