Anti-TPO Antibodies and Autoimmune Thyroid Disease#

Anti-TPO antibodies (also called anti-thyroid peroxidase antibodies) are made by the immune system when it attacks the thyroid gland by mistake. A high level points to autoimmune thyroid disease - most commonly Hashimoto's thyroiditis, which causes the thyroid to slowly become underactive over time.

A positive anti-TPO does not by itself mean you have thyroid disease today. It means your immune system is making antibodies that target your thyroid and that you have a higher chance of developing thyroid disease over the years.

Hashimoto's thyroiditis (also called chronic autoimmune thyroiditis) is the most common cause of an underactive thyroid in Canada. The immune system gradually damages the thyroid gland over years, so the gland slowly makes less thyroid hormone. About 90% of people with Hashimoto's thyroiditis have positive anti-TPO antibodies, although roughly 10% can test negative even when the disease is present.

Anti-thyroglobulin antibodies are another marker of autoimmune thyroid disease. They tend to overlap with anti-TPO and add little extra information in most cases. Most Canadian guidelines recommend anti-TPO over anti-thyroglobulin as the first-line autoimmune test.

Anti-TPO testing is most useful when:

• Your TSH is between 4 and 10 mIU/L with a normal Free T4 (subclinical hypothyroidism), and your clinician needs help deciding whether to start medication or monitor
• You have a strong family history of autoimmune thyroid disease and are deciding whether more frequent monitoring is reasonable
• You are planning pregnancy and have a borderline TSH

A positive anti-TPO in any of these situations supports earlier treatment or closer monitoring. A negative anti-TPO suggests it is reasonable to continue monitoring.

• If your TSH is normal and you have no symptoms or risk factors
• If you already have a confirmed diagnosis of an underactive thyroid - the cause is most likely autoimmune in Canada, so the result rarely changes management
• For monitoring over time - once positive, anti-TPO does not need to be repeated

Yes. Anti-TPO testing is available through TeleTest. It is usually billed as an uninsured (paid) test, because most provinces do not cover routine anti-TPO testing. You can add it when you book a thyroid panel.

No. Anti-TPO testing does not require fasting and is not affected by time of day.

Stop biotin (vitamin B7, sometimes labelled vitamin H) at least 72 hours before testing - high-dose biotin can interfere with thyroid antibody assays.

Each laboratory uses its own reference range, so the cut-off varies. Generally, a result clearly above the laboratory's upper limit is reported as "positive". A borderline (slightly elevated) result is more uncertain and may need to be repeated.

It means you have a higher lifetime risk of developing an underactive thyroid, but you do not have thyroid disease right now. The usual plan is to recheck your TSH every 1 to 2 years, or sooner if symptoms develop.

This combination raises the chance that your TSH will continue to climb into the clearly abnormal range. Many clinicians will:

• Start thyroid hormone medication if you have clear symptoms
• Recommend earlier treatment if you are pregnant or trying to conceive
• Otherwise monitor every 6 months

Yes. About 1 in 10 people with Hashimoto's thyroiditis test negative for anti-TPO. If your TSH is abnormal and Free T4 is low, the cause is still most likely autoimmune in Canada, even when antibodies are negative. A thyroid ultrasound can sometimes help when the picture is unclear, but this is usually done through your family doctor.

No. Once a positive result is documented, repeat testing does not change management. Antibody levels naturally fluctuate but the diagnosis does not change.

Yes - anti-TPO is more common in people with other autoimmune diseases like type 1 diabetes, vitiligo, celiac disease, lupus, and pernicious anemia. A positive anti-TPO does not mean you will develop those conditions, but the link is worth knowing.

Most provincial health plans do not cover anti-TPO as a routine test. There are some clinical situations where it is covered (such as evaluating subclinical hypothyroidism with planned pregnancy), but for most patients it will be billed as an uninsured test. The lab will collect the fee at the time of your visit.

Costs vary by lab and province. Contact your local lab directly for current pricing, or see your booking confirmation through TeleTest for the price applied to your order.