The features of hyperthyroidism are characteristic of the condition; however, certain laboratory tests help to firmly establish the diagnosis and also to determine the cause hyperthyroidism.

Some of the tests required for diagnosis are:

Thyroid hormone T3 and T4 levels: These will be higher than normal in cases of hyperthyroidism. T4 levels are high in the early stages whereas T3 levels rise in the later stages of the disease.

Thyroid Stimulating Hormone (TSH) level: This will be lower than normal in case of Hyperthyroidism since high levels of T3 and T4 in the blood provide a negative feedback to the pituitary thereby reducing the release of TSH.

Thyroid Scan with radioactive iodine: This shows whether the excess thyroid hormones are being secreted by the entire gland or one or more nodules (Hot Nodules) in the gland.

Iodine Uptake Scan: This test measures the amount of iodine that is taken up by the Thyroid gland. Patients with hyperthyroidism take up too much of iodine.

Thyroid Ultrasound: An ultrasound of the thyroid gland determines the presence of thyroid nodules and also whether they are solid or cystic (fluid-filled) in nature.

Thyroid stimulating immunoglobulin or TSI – the presence of thyroid stimulating antibodies indicates Graves' disease. In such cases, these immunoglobulins stimulate the thyroid to produce excess amounts of hormones resulting in a hyperthyroid state.