Overview
Quick answer
In Australia, thyroid antibody blood tests look for autoantibodies your immune system has made against thyroid tissue or proteins. The most common assay is thyroid peroxidase antibodies (TPO, also called anti-TPO). Results are reported in IU/mL, but the upper reference limit varies by laboratory and analyser. RCPA lists the reference interval as "consult pathologist" and notes low-titre positivity in up to 20% of the normal elderly population (TPO Ab page, last reviewed 2 January 2024).
Antibodies help explain an autoimmune thyroid pattern (Hashimoto or Graves) when the story or TSH already points that way. They are not a substitute for TSH and free T4, and they are not a routine Medicare screen for every asymptomatic adult. Medicare item 71165 covers one tissue antibody assay when clinically indicated (schedule fee $35.40 from 1 July 2025).
Hemexa includes TSH, free T4, and free T3 on the annual baseline. TPO and thyroglobulin antibodies (TgAb) are not on the Hemexa membership panel today. Your GP can order them through usual Medicare or private pathology when clinically indicated.
Overview
Key takeaways
TPO antibodies (anti-TPO) are the usual first antibody test in Australia. They target thyroid peroxidase, an enzyme the gland uses to make hormone.
Thyroglobulin antibodies (TgAb) are a second marker. TPO is generally more sensitive and specific for autoimmune thyroiditis than TgAb alone (Australian laboratory medicine summaries cite O'Leary 2006; Dwivedi et al. J Clin Pathol 2023).
Reports use IU/mL. Example upper limits on Australian lab handbooks range from under 5.61 IU/mL to under 34 IU/mL on different platforms. Use the interval on your own report, not a blog chart.
Positive TPO occurs in virtually all Hashimoto disease (RCPA). A positive result supports an autoimmune pattern; it does not by itself mean you must start thyroid hormone today.
Normal TSH with positive TPO is common. Many people are monitored over time; some never develop overt thyroid dysfunction. Rising TSH over repeat tests matters more than repeating the antibody titre.
Once TPO is positive, serial antibody monitoring is generally not useful (Australian clinical laboratory guidance). Track TSH and symptoms, not the antibody number every year.
Fasting is not required for antibody tests. High-dose biotin supplements can interfere with TPO/TgAb immunoassays; pause 48 to 72 hours before testing if your clinician agrees (same caution as the thyroid function guide).
Medicare 71165 funds one antibody assay when clinically indicated. Ordering both TPO and TgAb may bill as two items (71165 + 71166). Asymptomatic wellness antibody panels may be private out-of-pocket.
Graves disease often involves TSH receptor antibodies (TRAb/TSI), not the same test as TPO. Name the distinction; Hemexa does not catalogue TRAb or TSI assays.
Hemexa: TSH, free T4, and free T3 are on the annual panel among 76–80 signature markers. TPO and TgAb are not on the membership panel today.
Basics
What thyroid antibodies measure
Autoantibodies are immune proteins that mistakenly target your own tissue. In thyroid disease, they mark autoimmune attack on the gland or its proteins.
They are not the same as TSH (the pituitary signal), free T4 or free T3 (circulating hormone levels), or TSH receptor antibodies in Graves disease.
TPO (thyroid peroxidase)
Also called anti-TPO or anti-microsomal antibody in older literature. TPO is an enzyme in hormone synthesis. A positive result suggests the immune system is targeting that enzyme.
TgAb (thyroglobulin antibodies)
Thyroglobulin is the protein the gland uses to store hormone. TgAb targets that storage protein. It overlaps with TPO clinically but is a separate assay with its own reference interval.
A clue beside thyroid function tests
Pathology Tests Explained (updated 10 October 2025) states that presence of thyroid antibodies suggests autoimmune involvement; higher levels generally mean more likely autoimmune disease, but interpretation sits beside TSH, free T4, symptoms, and history.
A negative antibody result does not rule out all thyroid disease. A positive result does not replace thyroid function tests or, on its own, decide treatment.
Clinical patterns
Hashimoto, Graves, and normal TSH
Healthy people can be antibody-positive. Prevalence is higher in women and rises with age (Pathology Tests Explained). Pregnancy can change both antibody levels and fetal thyroid risk; trimester detail sits on the thyroid blood test guide.
Do not promise that lowering antibodies fixes symptoms. Treatment decisions follow hormone levels and clinical context, not the antibody titre alone.
| Pattern | Typical TFT | Antibodies | What this means |
|---|---|---|---|
| Hashimoto thyroiditis | High TSH, low free T4 (overt) or high-normal TSH (subclinical) | TPO positive (often TgAb too) | Autoimmune hypothyroid pattern; treatment follows TSH, symptoms, and pregnancy status |
| Graves disease | Low TSH, high free T4/T3 | TPO may be positive; TRAb/TSI drive hyperthyroidism | Name TRAb; this page does not cover antithyroid drug protocols |
| Euthyroid with positive TPO | TSH still in range | TPO positive | Common; watch TSH over time; no supplement protocol to clear antibodies |
If fatigue, hair thinning, or perimenopause overlap is in the picture, antibodies clarify thyroid autoimmunity but do not explain every symptom. See the always tired, hair loss, and perimenopause guides for those workups.
Reading your results
How to read an Australian report
Australian pathology reports label TPO and TgAb in IU/mL (international units per millilitre). Do not mix kIU/L labels without checking the report legend.
RCPA Manual TPO Ab lists the reference interval as "consult pathologist." Positive results occur in virtually all Hashimoto disease, with low titre in up to 20% of the normal elderly population (last reviewed 2 January 2024). Always compare to the interval printed on the same report.
TPO / anti-TPO / thyroid peroxidase Ab
Reported in IU/mL. Compare to this laboratory's cut-off, not a generic internet number.
TgAb / anti-thyroglobulin
Second marker in IU/mL with a method-specific interval. Alfred Health cites TgAb under 115 IU/mL on its handbook; Royal Melbourne cites under 4.11 IU/mL after its 2025 method change.
Negative / not detected
Does not rule out all thyroid disease. Some people with clinical hypothyroidism have negative antibodies.
Low-positive / borderline
May be clinically significant with family history, goitre, or a rising TSH. RCPA notes low-titre positivity in up to 20% of the normal elderly population.
Alfred Health (Melbourne): TPO under 34 IU/mL
Handbook cites under 34 IU/mL on Roche cobas ECLIA (testid 344). Also warns that biotin supplementation can interfere with TPO and TgAb on streptavidin-biotin immunoassays.
Royal Melbourne (TherMH): TPO under 5.61 IU/mL
Handbook cites under 5.61 IU/mL after Abbott Alinity i method change on 17 February 2025. Same platform lists TgAb under 4.11 IU/mL.
European multicentre illustration (not an Australian standard)
D'aurizio et al. (Clin Chem Lab Med 2015) reported manufacturer cut-offs for TPO across automated methods ranging from about 3.2 to 35 IU/mL. Use that only to show method dependence, not as a national Australian number.
Australian reports label TPO and TgAb in IU/mL. They are non-modifiable autoimmune markers when they appear on a result. Hemexa does not publish an optimal antibody band; do not read a preventative target into a positive titre.
Collection
Collection and biotin interference
RCPA TPO Ab asks for 5 mL blood in SST/serum. Fasting is not required for antibody tests alone (Pathology Tests Explained lists no special preparation).
When TSH is on the same request, morning collection is conventional for thyroid function tests, but antibodies alone do not need an overnight fast.
High-dose biotin supplements (often sold for hair and nails) can cause falsely high or low TPO and TgAb on streptavidin-biotin immunoassays. Pause high-dose biotin for 48 to 72 hours before testing if your clinician agrees. Do not diagnose from one interfered sample.
For TSH-first collection timing and the wider thyroid panel, see the thyroid blood test guide.
Indications
When GPs order antibody tests
Reasonable indications
- Family history of autoimmune thyroid disease or goitre
- Fluctuating or borderline TSH
- Other autoimmune conditions (type 1 diabetes, pernicious anaemia, and others)
- Persistent hypothyroid symptoms with equivocal thyroid function tests
- Hair loss pattern suggesting thyroid (temporal thinning, lateral eyebrow loss)
- Postpartum thyroiditis follow-up when your GP is already monitoring thyroid function
Generally not indicated
- Population screening of asymptomatic adults
- Annual wellness panels without a clinical story
- Replacing TSH because antibodies feel more root cause
- Serial TPO monitoring every year once already positive
Australian laboratory summaries usually start with TPO alone for autoimmune hypothyroidism workup. TgAb adds value when TPO is negative but suspicion remains, or in specific monitoring contexts such as thyroglobulin tumour-marker interference after thyroidectomy.
Markers
TPO vs thyroglobulin antibodies
TPO first
TPO is the first-line autoimmune marker in Australian practice. It is more sensitive and specific for autoimmune thyroiditis than TgAb alone in published comparisons (O'Leary 2006, cited in Australian Clinical Labs interpretation guidance; Dwivedi et al. 2023).
When TgAb adds value
TgAb may be added when TPO is negative with ongoing suspicion, or when thyroglobulin is used as a tumour marker after thyroid surgery. TgAb can interfere with thyroglobulin tumour-marker assays (Pathology Tests Explained).
Two MBS items if both are ordered
Ordering both antibodies on the same request may use Medicare item 71165 for one assay and 71166 for a second from the same list. Do not assume every private panel includes both by default.
Ordering through usual care
TPO and TgAb are standard Australian pathology assays when your GP adds them to a request. They are not on the Hemexa membership panel today.
How to order
How Australians get the test
| Approach | Best for | Typical cost | Includes antibodies? |
|---|---|---|---|
| GP-requested antibodies (Medicare) | Family history, goitre, borderline TSH, or other autoimmune disease | Bulk-billed or low gap when clinically indicated | Item 71165 (one antibody); 71166 (two on same episode) |
| GP thyroid panel with antibodies | TSH abnormal or symptoms with autoimmune suspicion | TSH often Medicare; antibodies may gap if indication unclear | TPO usual first; TgAb when clinically justified |
| Private antibody tests | When TFTs are already private or indication is borderline | Often $30 to $80 each if not Medicare-funded | TPO and/or TgAb as requested |
| Membership platforms (e.g. Hemexa) | Annual TSH, free T4, free T3 baseline; antibodies via GP when needed | ~$1,199/year (full membership) | TSH, free T4, free T3 on baseline; TPO/TgAb via GP order |
Pathology in Australia requires an authorised request from a registered medical practitioner. Collection is through Healius Pathology collection at 2,000+ centres (Healius Pathology, 2,000+ centres). For TSH-first pathways, costs, and morning collection, see the thyroid blood test guide. For Medicare episode rules beyond item 71165, see the Medicare blood tests guide.
FAQ
Frequently asked questions
- What are thyroid antibodies?
- They are autoantibodies against thyroid proteins. TPO (thyroid peroxidase) and thyroglobulin are the common blood tests in Australia, reported in IU/mL.
- What is a normal TPO antibody level in Australia?
- There is no single national number. Labs set method-specific cut-offs in IU/mL. RCPA lists consult pathologist. Example handbook limits on the same country range from under 5.61 IU/mL to under 34 IU/mL for TPO on different platforms. Use the reference interval on your report.
- Do I need to fast for a thyroid antibody test?
- No. Fasting is not required for TPO or TgAb alone. If the same visit includes fasting glucose or insulin, follow the fasting rule for the whole draw.
- What does a positive TPO result mean?
- It supports autoimmune thyroid disease, especially Hashimoto pattern, when read with TSH, free T4, symptoms, and history. It does not always mean you need treatment immediately.
- Can I have positive thyroid antibodies and a normal TSH?
- Yes. Many people do. Your GP usually monitors TSH over time rather than treating the antibody titre alone.
- Should I repeat TPO antibodies every year?
- Usually not once they are already positive. Repeat TSH and clinical review matter more than tracking the antibody level. Australian clinical laboratory guidance does not support serial TPO monitoring after a stable positive result.
- TPO vs thyroglobulin antibodies: which do I need?
- TPO is the usual first test. TgAb may be added when suspicion remains and TPO is negative, or for specific monitoring situations such as thyroglobulin tumour-marker interference.
- Does Medicare cover thyroid antibody tests?
- Item 71165 can rebate one tissue antibody assay when clinically indicated (schedule fee $35.40 from 1 July 2025). Item 71166 covers a second antibody from the same list on the same episode. Asymptomatic screening may be private. Check your request form and any insurer gap.
- Are thyroid antibodies tested in pregnancy?
- Yes, when clinically indicated. TPO antibodies can be checked in pregnancy when autoimmune thyroid disease is suspected, because positive TPO raises the risk of postpartum thyroiditis and may change monitoring. Trimester-specific TSH targets and treatment decisions sit on the thyroid blood test guide.
How Hemexa fits
How Hemexa can help
Thyroid antibodies clarify autoimmunity beside hormone levels. They belong on the request when the clinical story fits, not on every membership draw by default.
TSH, free T4, and free T3 on the annual baseline
Hemexa includes TSH, free T4, and free T3 on the 76–80 marker annual baseline among 76–80 signature markers. Results trend in the thyroid health-system dashboard.
TPO and TgAb through usual care
TPO and thyroglobulin antibodies (TgAb) are not on the Hemexa membership panel today. Your GP can order them through usual Medicare or private pathology when clinically indicated.
IU/mL reporting without an optimal antibody band
When ordered, antibodies report in IU/mL as non-modifiable autoimmune markers. Hemexa does not treat a positive TPO titre as a preventative target or prescribe protocols to clear antibodies.
GP-reviewed requests and Healius Pathology collection at 2,000+ centres
Hemexa coordinates authorised pathology requests and collection at 2,000+ centres nationwide through Healius Pathology, our only collection partner. Mention high-dose biotin before the draw; the member app flags a TPO and biotin interaction in biomarker links.
Sources
References
Royal College of Pathologists of Australasia. TPO Ab (RCPA Manual, reviewed 2 January 2024). View source ↗
Royal College of Pathologists of Australasia. Thyroglobulin Ab (RCPA Manual, reviewed 2 January 2024). View source ↗
Pathology Tests Explained. Thyroid antibodies (10 October 2025). View source ↗
Dwivedi SN et al. Thyroid autoantibodies. Journal of Clinical Pathology 2023;76:19-28. View source ↗
Royal College of Pathologists of Australasia. Thyroid function testing for adult diagnosis and monitoring (position statement, July 2017). View source ↗
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Educational information only. See the health disclaimer.