⚠️ Educational only. LabPlain does not provide medical advice or diagnosis. Always discuss your specific results with your healthcare provider.
What this test measures
TPO stands for thyroid peroxidase — an enzyme your thyroid gland uses to produce thyroid hormones. The TPO antibody test measures whether your immune system is producing antibodies that mistakenly attack this enzyme.
In a healthy immune system, antibodies only target foreign invaders like bacteria and viruses. In autoimmune thyroid disease, the immune system gets confused and attacks the thyroid's own proteins. Elevated TPO antibodies are the hallmark finding in Hashimoto's thyroiditis (the most common cause of hypothyroidism) and are also found in Graves' disease (the most common cause of hyperthyroidism).
Doctors order this test when evaluating unexplained thyroid problems, a goiter (enlarged thyroid), or symptoms that suggest an autoimmune thyroid condition — even when TSH and other thyroid hormone levels look normal.
Cutoffs vary by laboratory — always use the reference range on your specific lab report. Some labs report results simply as "negative" or "positive" rather than a number. A positive result means TPO antibodies were detected above the threshold considered normal for that lab's assay.
Having detectable TPO antibodies doesn't automatically mean you have a thyroid disease or that you'll develop one. About 10% of the general population has low-level TPO antibodies with no symptoms and normal thyroid function. Context and trends over time matter.
📌 Positive vs. elevated — what's the difference?
Many labs simply report TPO antibodies as positive or negative. If your result is positive, the key question is how positive — mildly elevated antibodies with normal TSH may be monitored, while very high antibodies with abnormal TSH are more likely to prompt treatment. Your doctor will look at the full picture.
What your result might indicate
↑ If Elevated (Positive)
Elevated TPO antibodies most often indicate Hashimoto's thyroiditis or Graves' disease. They may also be found in other autoimmune conditions. A positive result does not always mean your thyroid is currently malfunctioning — it means your immune system is targeting thyroid tissue.
✓ If Negative / Normal
A negative result makes autoimmune thyroid disease less likely, though it doesn't completely rule it out. Some people with Hashimoto's are "seronegative" — meaning they have the condition but don't produce detectable antibodies on standard tests.
Symptoms associated with TPO antibody conditions
↑ Hashimoto's (Underactive Thyroid)
Fatigue and sluggishness
Weight gain despite normal diet
Cold intolerance
Constipation
Dry skin and hair loss
Depression or brain fog
Slow heart rate
Puffy face or goiter
↑ Graves' Disease (Overactive Thyroid)
Unintentional weight loss
Rapid or irregular heartbeat
Heat intolerance and sweating
Anxiety and irritability
Tremor in hands or fingers
Frequent bowel movements
Bulging eyes (exophthalmos)
Enlarged thyroid (goiter)
Common causes of elevated TPO antibodies
Hashimoto's thyroiditis
This is by far the most common cause of elevated TPO antibodies. In Hashimoto's, the immune system slowly destroys thyroid tissue over years or decades. TPO antibodies are present in about 95% of people with Hashimoto's. The condition progresses slowly — many people have elevated antibodies for years before their thyroid function actually becomes abnormal. Once the thyroid can no longer compensate, TSH rises and hypothyroidism develops.
Graves' disease
Graves' disease is the leading cause of hyperthyroidism. While it's primarily identified by TSH receptor antibodies (TRAb), about 75% of people with Graves' disease also have elevated TPO antibodies. If your doctor suspects Graves', they'll likely order both antibody tests along with T3, T4, and a radioactive iodine uptake scan.
Other associations
TPO antibodies are also seen at higher rates in people with type 1 diabetes, rheumatoid arthritis, lupus, and other autoimmune diseases. Having one autoimmune condition increases the likelihood of developing others. Postpartum thyroiditis — a temporary thyroid inflammation after pregnancy — is also strongly associated with TPO antibodies.
Tests often ordered alongside TPO antibodies
TPO antibodies are always interpreted alongside other thyroid tests. Your doctor may also order:
TSH (Thyroid-Stimulating Hormone) — the primary screening test for thyroid function; elevated in hypothyroidism, suppressed in hyperthyroidism
Free T4 — measures active thyroid hormone; low in hypothyroidism, high in hyperthyroidism
Free T3 — the most biologically active thyroid hormone; often ordered when hyperthyroidism is suspected
Thyroglobulin antibodies (TgAb) — another autoimmune marker found in Hashimoto's; sometimes ordered alongside TPO antibodies
TSH receptor antibodies (TRAb) — specific to Graves' disease; ordered when hyperthyroidism is found
Thyroid ultrasound — imaging to assess thyroid size, texture, and look for nodules
What to do next
A positive TPO antibody result is a piece of the puzzle — not a complete diagnosis. If your thyroid function tests (TSH, Free T4) are currently normal, your doctor may recommend monitoring with annual bloodwork rather than starting treatment. If thyroid function is also abnormal, treatment decisions will follow. Hashimoto's with hypothyroidism is treated with levothyroxine (a synthetic thyroid hormone), while Graves' disease has several treatment options including medications, radioactive iodine, and surgery. The right path depends on your full picture — don't try to interpret this result in isolation.
Questions to ask your doctor
01My TPO antibodies are elevated — does that mean I have Hashimoto's or another autoimmune thyroid disease?
02My thyroid function looks normal right now — how often should I be retested?
03Should I also be tested for thyroglobulin antibodies or TSH receptor antibodies?
04Is a thyroid ultrasound recommended to look at the structure of my thyroid?
05Are there dietary or lifestyle changes that could reduce thyroid antibody levels?
06Should I be referred to an endocrinologist for ongoing management?
Frequently asked questions
Can I have elevated TPO antibodies and a completely normal thyroid?
Yes — this is actually common. Many people have elevated TPO antibodies for years, sometimes decades, before their thyroid function becomes abnormal. The antibodies indicate immune activity against the thyroid, but the thyroid can compensate for a long time. Regular monitoring is key so you catch any functional changes early.
Does a high TPO antibody number mean more severe disease?
Not necessarily. The absolute level of TPO antibodies doesn't reliably predict how severe the thyroid disease will be or how quickly it will progress. What matters more is whether your actual thyroid hormone levels are affected. Very high antibodies may prompt closer monitoring, but the number alone isn't a reliable severity indicator.
Can TPO antibody levels go down over time?
Yes, in some people they do — particularly after treatment of Graves' disease or with selenium supplementation, which has some evidence for modestly reducing TPO antibody levels in Hashimoto's. However, antibody levels fluctuate naturally, and a lower reading on one test doesn't always mean the underlying autoimmune process has resolved.
Is Hashimoto's disease serious?
Hashimoto's is a manageable chronic condition. The main risk is that the progressive immune attack on the thyroid eventually causes hypothyroidism — but once diagnosed, hypothyroidism is highly treatable with daily levothyroxine. With appropriate treatment and monitoring, most people with Hashimoto's live completely normal lives.
Is there a connection between TPO antibodies and pregnancy?
Yes, and it's important. Women with positive TPO antibodies before pregnancy have a higher risk of miscarriage, premature birth, and postpartum thyroiditis (a temporary thyroid inflammation after delivery). If you're pregnant or planning to become pregnant and have positive TPO antibodies, make sure your OB and endocrinologist are aware so thyroid function can be monitored closely throughout pregnancy.