TPO antibodies: normal range, high and low

In shortThere is no single numeric normal range: the laboratory compares the level with its own assay cutoff and reports a negative or positive result. Negative means the thyroid symptoms are probably not caused by an autoimmune disease; positive points toward Hashimoto's disease or Graves' disease.

Reference ranges

Group	Reference range
Normal result	negative — no thyroid peroxidase antibodies found

MedlinePlus defines a normal result as negative; numeric positivity cut-offs differ between assays and laboratories. International typical guidance, not a national standard.

Check your value

Enter your result — we will show how it compares with a typical range. Match the units of the selected row.

Approximate comparison with a typical range, not a diagnosis. Reference intervals vary by laboratory and method — check your report; result interpretation is done by a doctor.

What this marker is

A thyroid antibody test measures the level of thyroid antibodies in a blood sample. Antibodies are proteins that the immune system makes to fight foreign substances such as viruses and bacteria, but sometimes they attack the healthy cells of the body's own tissues by mistake — this is called autoimmune disease. When antibodies attack the thyroid, they can cause serious autoimmune thyroid diseases.

Two such diseases dominate. Hashimoto's disease, also known as Hashimoto's thyroiditis, is the most common cause of hypothyroidism, in which the thyroid does not make enough hormones and many of the body's functions slow down. Graves' disease is the most common cause of hyperthyroidism, in which the thyroid makes more hormones than the body needs and many functions speed up. If hypothyroidism or hyperthyroidism has already been diagnosed, thyroid antibody tests help find out whether an autoimmune disease is causing the problem.

There are different tests for different thyroid antibodies. High levels of thyroid peroxidase antibodies (TPOAb) are a sign that Hashimoto's disease is causing hypothyroidism; thyroglobulin antibodies (TgAb) are another sign of Hashimoto's; and thyrotropin receptor antibodies (TRAb) can be a sign of Graves' disease. According to ARUP Consult, TPOAb are present in more than 90% of people with Hashimoto's thyroiditis, and their presence is considered pathognomonic for it.

Unlike hormone tests, this result is qualitative: the laboratory reports it as negative or positive against its own cutoff, so no universal numeric reference range exists. TPOAb can also appear without current disease — they are found in up to 18% of pregnant women, where their presence predicts the risk of postpartum thyroiditis — and with subclinical hypothyroidism their presence may predict progression to overt hypothyroidism.

When it is high

Hashimoto's diseaseA positive result with TPOAb and/or TgAb may mean Hashimoto's disease — most people with Hashimoto's have high levels of one or both of these antibody types.

Graves' diseaseA positive result with TPOAb and/or TRAb may mean Graves' disease.

Quantity mattersThe more thyroid antibodies are found, the more likely it is that an autoimmune disorder of the thyroid is present.

Postpartum thyroiditis riskTPOAb are present in up to 18% of pregnant women, and their presence during pregnancy predicts the risk of thyroiditis after delivery.

Progression of subclinical hypothyroidismWhen TSH is mildly elevated with normal free T4, the presence of TPOAb may predict progression to overt hypothyroidism.

When it is low

A negative result is the expected findingWhen no thyroid antibodies are found, the thyroid symptoms are probably not caused by an autoimmune disease. Most healthy people have no detectable TPO antibodies.

What can skew the result

These factors can shift the value without any disease — worth considering before a retest:

The laboratory's own assay and cutoff — the result is read against the reference printed on the reportPregnancy — thyroid disease can get worse during pregnancy, and antibodies may be tested together with thyroid hormones

How to prepare

No special preparation is needed for a thyroid antibodies blood test.

When a retest makes sense

A positive result is read together with TSH, free T4, and free T3. If Hashimoto's disease or Graves' disease is diagnosed, medicines can manage the condition. During pregnancy, thyroid disease can get worse and harm both the mother and the unborn baby, so anyone who has ever had thyroid disease may be tested for thyroid antibodies along with thyroid hormones; medicines to treat thyroid disease are safe to take during pregnancy.

Who usually reviews this result

A result outside the reference range is usually reviewed by: an endocrinologist. Bring your lab report and any previous results to the appointment.

Names used on lab reports

Your report may use any of these names:
Anti-TPOTPOTPOAbThyroid peroxidase antibodyAntithyroid microsomal antibodyThyroid autoantibodies

Units

Measured in: IU/mL

Several markers on your report?

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Frequently asked questions

Why is there no normal range table on this page?

Because there is no universal numeric range for TPO antibodies. Each assay has its own cutoff, and the laboratory reports the result as negative or positive against that cutoff — the reference on the report is the one that applies.

Does a positive result prove autoimmune thyroid disease?

Not by itself. The more antibodies are found, the more likely an autoimmune thyroid disorder is, but the diagnosis also uses symptoms, medical and family history, an examination, and thyroid hormone tests such as TSH, free T4, and free T3.

Why are these antibodies tested during pregnancy?

Thyroid disease can get worse during pregnancy and harm both the mother and the unborn baby. Anyone who has ever had thyroid disease may be tested for thyroid antibodies along with thyroid hormone tests; medicines for thyroid disease are safe to take during pregnancy.

Sources

Thyroid Antibodies: MedlinePlus Medical Test — MedlinePlus, National Library of Medicine. Accessed: August 29, 2026.
Autoimmune Thyroiditis: ARUP Consult — ARUP Consult, ARUP Laboratories. Accessed: August 29, 2026.

TPO antibodies