Thyroid Peroxidase Antibodies (TPO)

TPO antibodies are a sign that your immune system may be attacking your thyroid gland, which can gradually affect how well your thyroid works. A result below the laboratory's reference limit is reassuring, while elevated levels mean your doctor should monitor your thyroid function regularly.

When elevated: Persistently elevated TPO-Ab, particularly at high titers, indicates active thyroid autoimmunity and confers a significantly increased risk of progressive thyroid failure; annual TSH monitoring is recommended in seropositive euthyroid individuals. In pregnancy, elevated TPO-Ab is associated with a 2–3-fold increased risk of miscarriage and a 30–50% risk of postpartum thyroiditis, warranting closer obstetric and endocrine surveillance. High TPO-Ab titers may also co-occur with other organ-specific autoimmune diseases (type 1 diabetes, celiac disease, Addison's disease), and clinical evaluation for associated conditions may be warranted. When low: Undetectable or very low TPO-Ab levels are generally reassuring and suggest the absence of thyroid-directed autoimmunity as a contributing mechanism to thyroid dysfunction. In patients with hypothyroidism and negative TPO-Ab, alternative etiologies—such as iodine deficiency, central hypothyroidism, thyroiditis of other causes, or medication effects—should be considered. There is no established clinical concern associated with very low or absent TPO-Ab levels.

TPO antibodies are not directly performance-related but matter for athlete health and longevity. Autoimmune thyroid disease can impair metabolism, energy production, and recovery; athletes with elevated TPO-Ab should work with their physician to monitor thyroid function (TSH, free T4) and optimize hormone status, as untreated hypothyroidism reduces endurance capacity and increases fatigue and injury risk.