The five thyroid tests include total T3 and T4, free T3 and T4, and thyrotropin-releasing hormone, or TSH. The five thyroid tests are used clinically to check thyroid function and are used to check for the following diseases: 1. Hypothyroidism, usually seen after major thyroidectomy, results in inadequate thyroid secretion, resulting in decreased T3, T4, and free T3 and T4 and increased TSH. 3. It is also commonly used in subacute thyroiditis and chronic lymphocytic thyroiditis to determine thyroid function. If thyroxine is low, further thyroxine supplementation therapy is required.