How are thyroid disorders evaluated?

How are thyroid disorders evaluated?

Thyroid disorders can be suspected based on a patient’s history, findings on physical examination, and/or abnormalities in routine laboratory tests. 

A thorough his-tory and physical examination are essential for evaluation and will assist in determining whether the patient is clini-cally euthyroid, hypothyroid, or hyperthyroid. Symptoms associated with hyperthyroidism and hypothyroidism are shown in Table 30.1. The physical examination should focus on the signs of hyperthyroidism and hypothyroidism (shown in Table 30.2), as well as the size and position of the thyroid, palpable nodules, and tracheal position.

Standard laboratory evaluations of thyroid function include TSH and free serum T₄ levels. Initially, an ultrasen-sitive TSH level is obtained and, if abnormal, then a free T₄ level is obtained. Because greater than 99% of circulating thyroid hormone is bound to thyroxine binding globulin (TBG), total T₄ levels may be deceiving. Increases in TBG (pregnancy, estrogen therapy) or decreases in TBG (cirrhosis,  nephrotic syndrome) may result in abnormal levels of total T₄ but normal levels of free T₄.

In hyperthyroidism, the TSH levels will be low and the T₄ levels will be high. If the serum T₄ level is normal, a T₃ level should be obtained. In hypothyroidism, the TSH level is high in intrinsic thyroid gland abnormalities or low in hypothalamic or pituitary gland abnormalities.

Imaging studies can be helpful in evaluating thyroid dis-orders. Radioactive thyroid uptake scans are important for determining whether thyroid nodules are active (“hot”) or inactive (“cold”). Hot nodules are rarely malignant. Ultrasound can be used to determine the size and number of thyroid nodules. CT scan or magnetic resonance imag-ing (MRI) will show the size of the thyroid, compression of neighboring structures, and the presence of lymph-adenopathy.