Thyroid Peroxidase (TPO) Ab

TPO antibodies are proteins your immune system makes that mistakenly attack your thyroid gland; having elevated levels means your immune system is active against your thyroid, which can increase the risk of thyroid problems over time even if your thyroid function is currently normal. Regular thyroid function monitoring is recommended if your TPO antibodies are elevated.

When elevated: Persistently elevated TPO Ab levels indicate active autoimmune thyroid inflammation and confer a significantly increased risk of developing hypothyroidism, with annual progression rates of 2–4% in euthyroid individuals and higher rates in those with concurrent subclinical hypothyroidism. High titers are also associated with adverse obstetric outcomes including miscarriage, preterm birth, and postpartum thyroiditis, making TPO Ab testing particularly relevant in women of reproductive age. In the setting of Graves' disease, elevated TPO Ab may predict a lower likelihood of sustained remission after antithyroid drug therapy. When low: Undetectable or low TPO Ab levels in a patient with suspected thyroid disease make autoimmune etiology less likely and should prompt consideration of other causes of thyroid dysfunction, such as iodine deficiency, subacute thyroiditis, or medication effects. Low or negative TPO Ab does not exclude autoimmune thyroid disease entirely, as a small proportion of patients with biopsy-confirmed Hashimoto's thyroiditis are seronegative. No clinical concern is associated with very low or undetectable TPO Ab levels in otherwise healthy individuals.

TPO antibodies are not directly performance-related, but autoimmune thyroid disease can impair aerobic capacity, recovery, and metabolic efficiency—issues that emerge gradually and may be mistaken for overtraining. Athletes with a family history of autoimmune thyroiditis or symptoms like persistent fatigue despite adequate rest may benefit from screening to catch thyroid dysfunction early and preserve training consistency.