| Patterns of changes in serum thyroid hormone and TSH levels due to nonthyroidal illnesses tend to differ from those in sick patients with concurrent hypothyroidism or hyperthyroidism (Figure 2). For example, in "euthyroid" patients with reduced TSH values due to nonthyroidal illnesses, total T4 and free T4 index values are typically normal or reduced, while in those with elevated TSH values, total T4 and free T4 index values are usually normal (3,10). In patients with hypothyroidism, the presence of thyroid autoantibodies may indicate autoimmune hypothyroidism. Serum reverse T3 concentrations do not reliably differentiate hypothyroid from "euthyroid" sick patients, and have questionable clinical utility (29). In patients with Graves' disease, thyroid stimulating immunoglobulin titers and thyroidal radioiodide uptake may be elevated, confirming the diagnosis. A radioiodide thyroid scan may differentiate between other causes of hyperthyroidism. Algorithms may be useful (6). |
