<prompt> Autoimmune thyroiditis can be confirmed in a patient byThyroid peroxidase antibody TPOAntinuclear antibodyThyroid uptake resinThyroid aspiration  <response>: Once hypothyroidism is diagnosed by clinical features, TSH and free T4 measurements, etiology can be confirmed by measuring the presence of autoantibodyparticularly thyroid peroxidase TPO, which is present in 90 to 95 of patients with autoimmune hypothyroidism. Biopsy by fine needle aspirate can confirm the diagnosis but is not necessary in most cases. 