Thyroid Antibodies (TPO & Thyroglobulin) Test
The Thyroid Antibodies Test measures serum thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TgAb), the principal autoantibodies in autoimmune thyroid disease. TPOAb is the most sensitive marker of Hashimoto thyroiditis and predicts progression in subclinical hypothyroidism;
2
Biomarkers
Blood (serum)
Sample
2–3 business days
Turnaround
No
Fasting
What is the Thyroid Antibodies test?
The Thyroid Antibodies Test measures serum concentrations of thyroid peroxidase and thyroglobulin antibodies, the two principal autoantibodies found in autoimmune thyroid disease. Practitioners order this test to confirm or exclude an autoimmune aetiology when thyroid dysfunction is present, to stratify the risk of progression in subclinical hypothyroidism, to identify pregnant women at risk of postpartum thyroiditis, and to assess thyroglobulin assay reliability in differentiated thyroid cancer surveillance. TPOAb is the more sensitive marker and the primary target when Hashimoto thyroiditis is suspected, while TgAb is measured alongside thyroglobulin in the cancer follow-up setting and adds diagnostic yield in the small proportion of autoimmune disease cases that are TPOAb-negative. The test does not replace thyroid-function testing — it is ordered to characterise the cause of abnormal TSH or free T4, not as a stand-alone screening tool in euthyroid asymptomatic individuals.
What does the Thyroid Antibodies test measure?
Thyroid peroxidase antibodies are IgG autoantibodies directed against thyroid peroxidase, the microsomal enzyme that catalyses iodination of thyroglobulin and coupling of iodotyrosines to form thyroxine and tri-iodothyronine. TPOAb are the hallmark of autoimmune thyroid disease, present in more than 90 per cent of patients with Hashimoto thyroiditis and in about 70 per cent of those with Graves disease. Antibody binding does not directly inhibit enzyme activity in vivo; rather, the presence of TPOAb marks lymphocytic infiltration and signals an ongoing autoimmune process that can progressively destroy thyroid follicular cells.
TPOAb is the single most sensitive marker of autoimmune thyroid disease and the preferred antibody for diagnostic confirmation of Hashimoto thyroiditis. Positive TPOAb predicts progression from subclinical to overt hypothyroidism, identifies pregnant women at increased risk of postpartum thyroiditis, and helps differentiate autoimmune from non-autoimmune causes of thyroid dysfunction. Serial titres are not recommended for routine monitoring, because antibody levels fluctuate independently of clinical course and do not guide therapy adjustments.
Thyroglobulin antibodies are IgG autoantibodies directed against thyroglobulin, the large glycoprotein scaffold upon which thyroid hormone synthesis occurs within follicular colloid. TgAb are present in about 60–80 per cent of Hashimoto thyroiditis and in a smaller proportion of Graves disease. More importantly, TgAb interfere with thyroglobulin immunoassays, causing falsely low or falsely high thyroglobulin measurements depending on assay architecture. For this reason TgAb must always be measured alongside serum thyroglobulin when thyroglobulin is used as a tumour marker in differentiated thyroid cancer surveillance.
TgAb serves two roles: as a marker of autoimmune thyroid disease (though less sensitive than TPOAb) and as an essential quality-control check when measuring serum thyroglobulin. In thyroid cancer follow-up, positive TgAb renders thyroglobulin unreliable, and the trend of TgAb titre itself can serve as a surrogate tumour marker. In autoimmune thyroid disease diagnosis, TgAb adds little when TPOAb is already positive, but about 5–10 per cent of Hashimoto patients are TPOAb-negative yet TgAb-positive, so both antibodies are often ordered together.
Why is the Thyroid Antibodies test ordered?
- Confirmation of autoimmune thyroid disease in patients with overt or subclinical hypothyroidism, goitre, or thyrotoxicosis
- Risk stratification and prediction of progression to overt hypothyroidism in patients with isolated TSH elevation and normal free T4
- First-trimester assessment in women with a personal or family history of autoimmune thyroid disease, to identify risk of pregnancy complications and postpartum thyroiditis
- Differentiated thyroid cancer surveillance, measured alongside serum thyroglobulin to detect assay interference and to use TgAb titre as a surrogate tumour marker when positive
- Evaluation of subclinical or overt hypothyroidism in the postpartum period, where autoimmune thyroiditis is the commonest cause
- Work-up of thyroid nodules or goitre when ultrasound features raise suspicion of chronic lymphocytic thyroiditis
- Investigation of unexplained infertility or recurrent miscarriage, where thyroid autoimmunity is an independent risk factor even in euthyroid women
- Baseline assessment before starting amiodarone, lithium, immune-checkpoint inhibitors, or interferon, as pre-existing thyroid autoimmunity increases the risk of drug-induced thyroid dysfunction
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
2–3 business days
Collection notes
Phlebotomy at the processing lab's draw site (LabCorp or Quest, depending on routing); no special preparation required. Document high-dose biotin use, which can interfere with some immunoassays — advise discontinuation at least 48–72 hours before the draw. For serial assessment, use the same laboratory and assay, as cut-offs differ between methods. Where thyroglobulin is measured as a cancer tumour marker, thyroglobulin antibodies must be measured on the same sample.
Specimen requirements
Minimum 0.5 mL serum (gel separator acceptable). Separate from cells and refrigerate if not assayed promptly. Note the performing laboratory and assay platform for serial comparability.
What can affect Thyroid Antibodies results?
Biotin interferes with streptavidin-biotin immunoassays, causing falsely low or falsely high antibody results depending on assay architecture. Discontinue biotin at least 48–72 hours before the draw.
Cut-offs, detection ranges, and susceptibility to interference differ between immunoassay systems (Roche, Abbott, Siemens, Beckman). Serial measurements should use the same laboratory and method for valid comparison.
Circulating immunoglobulins can bind assay antibodies and cause spurious results; repeat testing with blocking reagents or an alternative method if the result is discordant with clinical presentation.
Removal or destruction of thyroid tissue can reduce antigen load and, over months to years, lead to declining antibody titres. In cancer surveillance, falling TgAb may reflect successful therapy or loss of antigenic stimulus.
High-dose corticosteroids, rituximab, and other immunosuppressants can transiently lower antibody titres, but this does not reflect resolution of autoimmune disease and titres typically rebound after treatment.
Maternal immune tolerance during pregnancy can transiently suppress thyroid antibody levels, which often rebound postpartum and may trigger postpartum thyroiditis.
What do Thyroid Antibodies results mean?
Elevated
Positive TPOAb confirms autoimmune thyroid disease — Hashimoto thyroiditis if hypothyroid, Graves disease if thyrotoxic (though TSH-receptor antibodies are more specific for Graves). Positive TgAb also supports autoimmune aetiology and, when present in cancer surveillance, indicates that serum thyroglobulin is unreliable and that TgAb titre itself should be followed. The magnitude of antibody elevation does not correlate tightly with disease severity, and serial monitoring of titres is not routinely recommended outside the cancer-surveillance setting.
Normal
Negative thyroid antibodies make autoimmune thyroid disease less likely but do not exclude it. In subclinical hypothyroidism, negative antibodies lower (but do not eliminate) the risk of progression to overt disease. In the cancer-surveillance setting, negative TgAb confirms that serum thyroglobulin can be interpreted without antibody interference.
Reduced
Undetectable or low antibody levels do not exclude all autoimmune thyroid disease — seronegative Hashimoto exists, diagnosed by ultrasound and clinical features. Falling titres after thyroid surgery or ablation may reflect loss of antigenic drive; in the cancer setting, this can be a favourable sign but must be interpreted with imaging and clinical context.
Note: Antibody status is a snapshot; low-titre positivity can fluctuate across the cut-off. TPOAb and TgAb do not perfectly overlap — test both when diagnostic certainty is required. Serial antibody monitoring does not guide treatment decisions in autoimmune thyroid disease, with the exception of TgAb trending in thyroid cancer follow-up. Method-specific cut-offs mean that results from different laboratories are not directly comparable.
Frequently asked questions
Both are autoantibodies in thyroid disease, but TPOAb (thyroid peroxidase antibody) is more sensitive and the preferred marker for Hashimoto thyroiditis, while TgAb (thyroglobulin antibody) is measured primarily to check for interference in thyroglobulin cancer-surveillance assays and as a second antibody when TPOAb is negative.
How to access the Thyroid Antibodies test
The Thyroid Antibodies reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Pearce SHS, et al. 2013 ETA guideline: management of subclinical hypothyroidism. Eur Thyroid J. (2013)
- Alexander EK, et al. 2017 guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum. Thyroid. (2017)
- Haugen BR, et al. 2015 American Thyroid Association management guidelines for adult patients with thyroid nodules and differentiated thyroid cancer. Thyroid. (2016)
- Pyzik A, et al. Immune disorders in Hashimoto's thyroiditis: what do we know so far? J Immunol Res. (2015)
- Spencer CA, et al. Thyroglobulin antibody (TgAb) methods — strengths, pitfalls and clinical utility for monitoring TgAb-positive patients with differentiated thyroid cancer. Best Pract Res Clin Endocrinol Metab. (2013)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.