endocrine and metabolic disorders
Hyperthyroidism
Diagnosis of Hyperthyroidism
TSH Free T4, plus either free T3 or total T3 Sometimes radioactive iodine uptake Diagnosis of hyperthyroidism is based on history, physical examination, and thyroid function tests. Serum TSH measurement is the best test because TSH is suppressed in hyperthyroid patients except in the rare instance when the etiology is a TSH-secreting pituitary adenoma or pituitary resistance to the normal inhibition by thyroid hormone. Free T4 is increased in hyperthyroidism. However, T4 can be falsely normal in true hyperthyroidism in patients with a severe systemic illness (similar to the falsely low levels that occur in Euthyroid Sick Syndrome ) and in T3 toxicosis. If free T4 level is normal and TSH is low in a patient with subtle symptoms and signs of hyperthyroidism, then serum T3 should be measured to detect T3 toxicosis; an elevated level confirms that diagnosis. The cause can often be diagnosed clinically (eg, the presence of signs specific to Graves disease). If not, radioactive iodine uptake by the thyroid may be measured by using iodine-123. When hyperthyroidism is due to hormone overproduction, radioactive iodine uptake by the thyroid is usually elevated. When hyperthyroidism is due to thyroiditis, iodine ingestion, or overtreatment with thyroid hormones, radioactive iodine uptake is low. TSH receptor antibodies can be measured to evaluate for Graves disease. Measurement is done in pregnant women with a history of Graves disease during the 3rd trimester of pregnancy to assess the risk of Hyperthyroidism in Infants and Children ; TSH receptor antibodies readily cross the placenta to stimulate the fetal thyroid. Most patients with Graves disease have circulating antithyroid peroxidase antibodies, and fewer have antithyroglobulin antibodies. Inappropriate TSH secretion is uncommon. The diagnosis is confirmed when hyperthyroidism occurs with elevated circulating free T4 and T3 concentrations and normal or elevated serum TSH. If thyrotoxicosis factitia is suspected, serum thyroglobulin can be measured; it is usually low or low-normal—unlike in all other causes of hyperthyroidism. Subclinical hyperthyroidism is low serum TSH in patients with normal serum free T4 and T3 and absent or minimal symptoms of hyperthyroidism. Subclinical hyperthyroidism is far less common than Subclinical hypothyroidism . . The other causes of subclinical hyperthyroidism are the same as those for clinically apparent Etiology . Patients with serum TSH<0.1 microU/mL (0.1 mU/L) have an increased incidence of atrial fibrillation (particularly older patients), reduced bone mineral density, increased fractures, and increased mortality. Patients with serum TSH that is only slightly below normal are less likely to have these features. 