Test Background TPO is the immuno-active microsomal antigen. TPO antibodies are measured in patients with suspected hypothyroidism or hyperthyroidism. TPO is present in 50-80 % of Graves’ disease patients and in 80-95 % patients with Hashimoto’s thyroiditis (usually at high titres). 15 % of healthy females over the age of 40 also have these antibodies.
Clinical Indications To identify an autoimmune cause for primary hypothyroidism
To identify the risk of progression to overt hypothyroidism in patients with borderline thyroid function tests (for individuals with TSH excess or mild thyroid failure, a positive TPO antibody indicates an approximate two-fold increase in risk of progression to overt hypothyroidism)
Prior to treatment with medication that may precipitate hypothyroidism
In pregnant women as a predictor of potential intrapartum hypothyroidism