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Thyroid peroxidase antibody Test

Thyroid peroxidase antibody Test

January 21, 2026
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Do I need a Thyroid peroxidase antibody test?

Struggling with unexplained fatigue, weight changes, or feeling unusually cold? Could your immune system be attacking your thyroid, and might testing for thyroid peroxidase antibodies reveal what's happening?

Thyroid peroxidase antibodies indicate whether your immune system is targeting your thyroid gland, which can disrupt hormone production and leave you feeling off. Elevated levels often point to autoimmune thyroid conditions like Hashimoto's thyroiditis.

Testing your TPO antibodies gives you a vital snapshot of your thyroid health, helping pinpoint whether autoimmunity is driving your fatigue, weight struggles, or temperature sensitivity. This clarity empowers you to personalize your treatment plan and take meaningful steps toward feeling better.

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Key benefits of Thyroid peroxidase antibody testing

  • Reveals if your immune system is attacking your thyroid gland.
  • Flags autoimmune thyroid disease before symptoms become severe or irreversible.
  • Explains unexplained fatigue, weight changes, or mood shifts tied to thyroid dysfunction.
  • Guides treatment decisions when thyroid hormone levels sit in borderline zones.
  • Protects fertility by identifying autoimmune risk that may affect conception or pregnancy.
  • Tracks disease activity over time to adjust therapy and prevent complications.
  • Best interpreted with TSH, Free T4, and your clinical symptoms for full context.

What is Thyroid peroxidase antibody?

Thyroid peroxidase antibody (TPO antibody) is an immune protein produced by your body's defense system that mistakenly targets thyroid peroxidase, a key enzyme inside your thyroid gland. Thyroid peroxidase is essential for making thyroid hormones, which regulate your metabolism, energy, and growth. When TPO antibodies are present, they signal that your immune system has identified your own thyroid tissue as foreign.

Your immune system turning on itself

The presence of TPO antibodies indicates autoimmune activity against the thyroid. These antibodies can interfere with thyroid peroxidase's normal function, disrupting hormone production over time. They are the hallmark of autoimmune thyroid conditions, where the body's protective mechanisms become misdirected.

A window into thyroid inflammation

TPO antibodies reflect ongoing or potential thyroid inflammation. Their presence often precedes or accompanies changes in thyroid function, making them a valuable marker of autoimmune thyroid disease.

Why this antibody matters

Detecting TPO antibodies helps identify the underlying cause of thyroid dysfunction. It distinguishes autoimmune processes from other thyroid problems, guiding understanding of what's happening inside your thyroid gland.

Why is Thyroid peroxidase antibody important?

Thyroid peroxidase antibody (TPO-Ab) reveals whether your immune system is mistakenly attacking your thyroid gland, the metabolic control center in your neck. This antibody targets the enzyme that helps produce thyroid hormones, which regulate energy, temperature, heart rate, digestion, mood, and reproductive function. Elevated TPO-Ab signals autoimmune thyroid disease, most commonly Hashimoto's thyroiditis or Graves' disease, and predicts future thyroid dysfunction even when hormone levels still appear normal.

When antibodies stay quiet

In healthy individuals, TPO-Ab levels remain undetectable or very low, typically below 35 IU/mL depending on the lab. This reflects a thyroid free from autoimmune attack. The gland produces hormones smoothly, supporting stable metabolism and energy throughout the body.

When the immune system turns inward

Elevated TPO-Ab indicates ongoing autoimmune inflammation within the thyroid. Over months to years, this can destroy thyroid tissue, leading to hypothyroidism with fatigue, weight gain, cold intolerance, constipation, brain fog, and depression. Women are five to eight times more likely to develop thyroid autoimmunity than men, especially during reproductive years and after pregnancy. High antibody levels during pregnancy increase risk of postpartum thyroiditis and miscarriage.

The long view on thyroid immunity

TPO-Ab serves as an early warning system, often appearing years before thyroid hormone imbalance becomes clinically apparent. Monitoring this biomarker helps anticipate progression to overt disease, assess cardiovascular and metabolic risk, and understand fertility challenges in women of childbearing age.

What do my Thyroid peroxidase antibody results mean?

Low or undetectable values

Low values usually reflect the absence of autoimmune activity against the thyroid gland. Thyroid peroxidase antibodies are proteins made by the immune system that mistakenly target thyroid peroxidase, an enzyme essential for producing thyroid hormone. When these antibodies are absent or very low, the thyroid is not under immune attack, and hormone production can proceed normally. This is the expected finding in most healthy individuals.

Optimal range

Being in range suggests no significant autoimmune thyroid disease. Most laboratories define normal as undetectable or very low levels of thyroid peroxidase antibodies. There is no advantage to having any measurable amount, so optimal sits at the lowest detectable limit. This reflects immune tolerance to thyroid tissue and stable thyroid function over time.

Elevated values

High values usually reflect autoimmune thyroid disease, most commonly Hashimoto thyroiditis or Graves disease. The antibodies interfere with thyroid peroxidase function and promote inflammation within the thyroid gland, often leading to gradual destruction of thyroid tissue and eventual underproduction of thyroid hormone. Women are affected more often than men, and prevalence increases with age. Elevated antibodies during pregnancy raise the risk of postpartum thyroiditis and may influence fetal thyroid development.

Factors that influence results

Antibody levels can fluctuate over time and may rise during periods of stress or illness. Some individuals have persistently elevated antibodies without overt thyroid dysfunction for years.

Method: FDA-cleared clinical laboratory assay performed in CLIA-certified, CAP-accredited laboratories. Used to aid clinician-directed evaluation and monitoring. Not a stand-alone diagnosis.

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Frequently Asked Questions

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How it works
What should I expect during a blood draw?
  • A trained phlebotomist will guide you through the process.
  • A tourniquet is placed on your arm, the site is cleaned, and a small needle is used to collect blood into one or more tubes.
  • Results are usually ready in about a week.
  • Most people feel only a quick pinch.
  • The needle is removed, gentle pressure is applied, and a bandage is placed.
How do I prepare for a blood draw?
  • Drink plenty of water beforehand — hydration makes veins easier to find.
  • Wear loose sleeves so your arm is easy to access.
  • Follow any fasting instructions you’ve been given.
  • Let us know if you’re on medications, have fainted before, or have needle anxiety.
What should I do after my blood draw?
  • Press gently on the site for a few minutes.
  • Keep the bandage on for 4-6 hours.
  • Skip heavy lifting or strenuous exercise for the rest of the day.
  • Drink extra water to rehydrate.
  • Monitor the site for redness, swelling, or pain.
How do I book a blood draw with Superpower?

Your membership includes:

  • An annual full body test and report across 100+ biomarkers
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Many concierge clinics charge $10k – $100k for their services, we’ve built technology to make the world’s best healthcare as accessible as possible via an all-in-one membership.

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Superpower is currently available in the following US states:

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While you will have a Superpower care team, your annual membership is designed to complement a primary care doctor if you have one, not replace them.

We are happy to help you share any test results with an outside provider to ensure you receive well-rounded medical care.

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Your annual lab test panel takes about a week to process. We will text you as soon as they become available in your dashboard. Other types of tests may have different testing windows. The Superpower concierge is your own health assistant who helps answer your questions on your results, ensure smooth scheduling, coordination of any office-based tests, specialist referrals as needed, and navigating you to interface with your care team.

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Superpower membership and products are all eligible for HSA/FSA funding.

We see Superpower like a gym membership for those committed to prevention and performance. Superpower is a bridge between wellness and healthcare. Health insurance traditionally focuses on reactive care whereas, at Superpower, we believe it’s never too early to start looking out for your long-term health.

What if I want more than 1 blood test per year?

Absolutely — you're not limited to just one. Your membership includes one comprehensive 100+ biomarker blood test each year, but if you'd like to track your progress more closely, you can add extra tests at any time. Each additional full-panel test costs $179. You can order as many as you'd like throughout the year.

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Frequently Asked Questions about Thyroid peroxidase antibody Test

What is a thyroid peroxidase antibody (TPO antibody) test and what does it measure?

A thyroid peroxidase antibody (TPO-Ab) test measures immune proteins that mistakenly target thyroid peroxidase, an enzyme your thyroid uses to make thyroid hormones. When TPO antibodies are present, they signal autoimmune activity against the thyroid gland and often reflect thyroid inflammation. This helps identify whether thyroid dysfunction is likely autoimmune (such as Hashimoto’s thyroiditis or sometimes Graves’ disease) rather than due to a non-autoimmune cause.

Why would my doctor order thyroid peroxidase antibody testing for fatigue, weight changes, or mood symptoms?

TPO antibody testing can help explain unexplained fatigue, weight gain, brain fog, depression, or mood shifts when thyroid dysfunction is suspected. Elevated TPO-Ab suggests autoimmune thyroid disease that can gradually impair hormone production over time. It’s especially useful when symptoms are present but thyroid hormone levels are borderline, because it reveals whether the immune system is actively attacking thyroid tissue and predicts risk of future hypothyroidism.

What is a normal thyroid peroxidase antibody level and what does “below 35 IU/mL” mean?

Most labs consider TPO antibodies normal when they’re undetectable or below a cutoff, commonly under 35 IU/mL. In healthy individuals, TPO-Ab is absent or very low, reflecting immune tolerance toward the thyroid. “Optimal” is essentially near zero, since any measurable antibody can indicate some immune activation. Normal/low results suggest there is no active autoimmune attack on the thyroid, and other causes of thyroid symptoms may be considered.

What does it mean if my thyroid peroxidase antibody level is high (including very high results over 1,000 IU/mL)?

High TPO-Ab usually indicates autoimmune thyroid disease - most commonly Hashimoto’s thyroiditis, and less often Graves’ disease. Very high levels (sometimes above 1,000 IU/mL) often correlate with more significant thyroid inflammation and risk of progressive thyroid damage. Even if TSH and Free T4 are still normal, elevated antibodies can predict future hypothyroidism over months to years and help explain symptoms tied to thyroid dysfunction.

How do TPO antibodies affect thyroid hormone production and metabolism over time?

TPO antibodies target thyroid peroxidase, an enzyme required for thyroid hormone production. This autoimmune activity can interfere with normal thyroid function and contribute to ongoing inflammation. Over time, thyroid hormone output may decline, leading to hypothyroidism and symptoms like fatigue, cold intolerance, constipation, dry skin, weight gain, hair thinning, and menstrual irregularities. Because thyroid hormones influence energy use, heart rate, digestion, temperature, and mood, long-term autoimmune damage can affect many organ systems.

How should thyroid peroxidase antibody results be interpreted with TSH and Free T4?

TPO antibodies are best interpreted alongside TSH, Free T4, and your clinical symptoms. TPO-Ab identifies autoimmune activity, while TSH and Free T4 show how well the thyroid is currently maintaining hormone levels. You can have high antibodies with normal hormones early on, which signals risk for future dysfunction. In borderline thyroid labs, a positive TPO-Ab result can guide treatment decisions and monitoring frequency by clarifying that autoimmunity is driving the pattern.

Can thyroid peroxidase antibodies impact fertility, conception, or pregnancy outcomes?

Yes. Elevated TPO-Ab can flag autoimmune thyroid risk that may affect fertility and pregnancy, even before hormone levels shift dramatically. In pregnancy, high TPO antibodies are associated with increased risk of miscarriage, preterm birth, and postpartum thyroiditis. Because thyroid hormones support reproductive function and fetal development, identifying TPO-Ab can prompt closer monitoring of thyroid status (often with TSH and Free T4) to protect conception and pregnancy outcomes.

Why do TPO antibody levels change during pregnancy and postpartum, and does that affect interpretation?

TPO antibody levels can rise or fall over time and may fluctuate independently of symptoms. Pregnancy often suppresses immune activity, which can temporarily lower TPO-Ab levels, while the postpartum period can trigger a rebound surge in autoimmunity. This matters because a “lower” pregnancy result may not reflect long-term risk, and postpartum increases can coincide with postpartum thyroiditis. Interpreting results with timing, symptoms, and thyroid labs (TSH, Free T4) improves accuracy.

If my TPO antibodies are high but I feel fine, does that still matter?

High TPO-Ab can matter even without symptoms because it often precedes measurable thyroid hormone changes. Elevated antibodies indicate autoimmune thyroid inflammation and predict increased risk of developing hypothyroidism over time, especially during hormonal shifts like pregnancy or menopause. The antibodies don’t always cause immediate symptoms, but they can guide proactive monitoring and early intervention to help preserve thyroid function and prevent complications related to metabolism, mood, cardiovascular risk, and reproductive health.

What are common misconceptions about thyroid peroxidase antibodies and autoimmune thyroid disease?

A common misconception is that TPO antibodies alone diagnose hypothyroidism; they don’t - TSH, Free T4, and symptoms show current thyroid function. Another misconception is that a single antibody number always matches symptom severity; TPO-Ab can vary by assay and fluctuate over months to years. It’s also incorrect to assume normal thyroid hormones mean “no risk” if antibodies are high; elevated TPO-Ab can signal early autoimmune thyroid disease before labs shift.

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