How is hyperthyroidism commonly diagnosed?

In diagnosing hyperthyroidism, measuring serum levels of Thyroid Stimulating Hormone (TSH) and Thyroxine (T4) is the most common and effective method. In hyperthyroidism, there is often a decrease in TSH levels due to the negative feedback mechanism because excess thyroid hormones (T4 and T3) inhibit the pituitary gland's release of TSH. Simultaneously, T4 levels are typically elevated in hyperthyroid patients. This combination of TSH and T4 level assessment provides a clear indication of thyroid function and helps in confirming the diagnosis of hyperthyroidism.

In contrast, while other methods might have their place in further evaluation or in different contexts, they do not serve as the primary diagnostic tool. Ultrasound imaging may be useful in assessing thyroid nodules or structural abnormalities but does not quantify thyroid hormone levels. Clinical symptoms can suggest hyperthyroidism but are not definitive for diagnosis, as symptoms may overlap with other conditions. Finally, a biopsy of thyroid tissue is generally not part of the initial diagnosis of hyperthyroidism and is reserved for evaluating thyroid cancers or suspicious nodules. Thus, measuring serum levels of TSH and T4 is the cornerstone of diagnosing hyperthyroidism accurately.