The main hormone produced by the thyroid gland, precursor to T3.

The active form of thyroid hormone that helps maintain metabolism and energy levels among many other functions.

Measures the inactive form of T3. Elevated levels can be seen in non-thyroidal illness syndrome (euthyroid sick syndrome) and can help differentiate between different types of thyroid dysfunction.

Assesses the binding capacity of thyroid hormone-binding proteins. It is used to calculate the free thyroxine index (FTI), which helps in evaluating thyroid function by accounting for variations in binding proteins.

Measures the level of TBG, the main protein that binds thyroid hormones in the blood. Abnormal levels can affect total T4 and T3 measurements and can be seen in conditions like pregnancy, liver disease, and certain medications.

High levels of TPO antibodies are indicative of autoimmune thyroid diseases such as Hashimoto's thyroiditis and Graves' disease. They are often measured when TSH levels are abnormal to assess for autoimmune etiology.

Elevated levels of thyroglobulin antibodies are also associated with autoimmune thyroid diseases, particularly Hashimoto's thyroiditis. They can be measured when TPO antibodies are negative but clinical suspicion for autoimmune thyroiditis remains.