Thyroid Peroxidase Antibodies (TPO-AB)

What are Thyroid Peroxidase Antibodies?

TPO antibodies are autoimmune markers that target thyroid peroxidase, an enzyme essential for thyroid hormone production. Their presence indicates that the immune system is attacking the thyroid gland, which is characteristic of autoimmune thyroid conditions like Hashimoto’s thyroiditis and Graves’ disease.

Why is it Tested?

Doctors order TPO antibodies to diagnose autoimmune thyroid disease, investigate unexplained thyroid dysfunction, and assess risk for future thyroid problems. It’s particularly useful for distinguishing autoimmune causes from other forms of thyroid disease.

Normal Ranges

Reference ranges vary by lab but generally:

Normal: <34 IU/L

Values above this threshold suggest autoimmune thyroid disease, with higher levels indicating more significant antibody presence.

Reference ranges vary by authority. Track yours across multiple standards with automatic unit conversions in LabsVault.

What do Abnormal Results Mean?

Abnormal results are not a diagnosis. Always discuss your results with a qualified healthcare provider before making any medical decisions.

Normal TPO Antibodies

Normal levels suggest:

No significant autoimmune thyroid disease
Lower risk of future thyroid dysfunction
Non-autoimmune causes if thyroid problems exist

High TPO Antibodies

Elevated antibodies may indicate:

Hashimoto’s thyroiditis
Graves’ disease
Increased risk of future hypothyroidism
Postpartum thyroiditis
Other autoimmune conditions

How to Track Over Time

TPO antibody levels can fluctuate but typically remain elevated once positive. Tracking levels helps monitor disease progression, assess treatment response, and predict the likelihood of developing overt thyroid dysfunction. Rising antibody levels may precede clinical symptoms by years.

Thyroid Peroxidase Antibodies