One-Page on TPO Antibodies
Thyroid-peroxidase antibodies (TPO antibodies, also called anti-TPO antibodies) are highly specific for autoimmune thyroid diseases, namely Hashimoto's thyroiditis and Graves' disease.
TPO antibodies are present in 95% of cases of Hashimoto's thyroiditis, the commonest cause of hypothyroidism in iodine-sufficient areas.
TPO antibodies are present in about 70-80% of patients with Graves' disease. However, another antibody, the thyrotropin receptor antibody (TRAb), is much more specific for Graves'.
TPO antibodies are present in 10-15% of the general population, more in women than men. This euthyroid population has a greater probability of developing hypothyroidism.
The higher the TPO antibody titer in a euthyroid person, the greater the chance of developing hypothyroidism.
Family members of persons with elevated TPO antibodies have a greater chance of having abnormal levels, too.
The greatest utility of TPO antibody testing is in subclinical hypothyroidism because their presence influences treatment decisions and predicts progression to overt hypothyroidism at a rate of 4.3% per year versus 2.6% per year when TPO antibodies are negative.
Persons with subclinical hypothyroidism (TSH 5 to 10 with normal T3/T4) and abnormal TPO antibodies should be given thyroxine if pregnant or planning conception.
In patients with known overt hypothyroidism, measurement of anti-TPO antibodies is not required.
Anti-TPO antibody testing should never be performed when TSH is normal except in specific circumstances involving pregnancy.
TPO antibodies are tested in euthyroid women desirous of pregnancy in three situations - recurrent pregnancy loss, infertility evaluation, strong family history of hypothyroidism.
Women who are TPO antibody-positive and a normal prepregnancy TSH should have TSH measured at pregnancy confirmation and every 4 weeks through midpregnancy, and then once at 32 weeks. About 20% of such cases will develop elevated TSH during gestation.
TPO antibody positivity is a risk factor for developing hypothyroidism during treatment with lithium or amiodarone
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