What this test measures
Anti-Microsomal Antibody (AMA) is the older name for anti-thyroid peroxidase antibody (anti-TPO). Thyroid peroxidase is an enzyme on thyroid follicular cells that helps produce thyroid hormones. In autoimmune thyroid disease, the immune system makes antibodies against this enzyme, gradually damaging the thyroid and changing its hormone output.
The test is a quantitative immunoassay reported in IU/mL. A positive result indicates autoimmune thyroid disease — most commonly Hashimoto's thyroiditis (which causes hypothyroidism) and less often Graves' disease (which causes hyperthyroidism). Anti-TPO is the most sensitive single antibody for autoimmune thyroid disease and is detected in over 90% of Hashimoto's and ~75% of Graves' patients.
Why it matters
Autoimmune thyroid disease is the most common autoimmune condition worldwide and is strikingly common in Indian women, with prevalence estimates of 8–11% in some regions. Many patients are diagnosed only after years of fatigue, weight changes, irregular periods, hair loss, or infertility. A positive AMA / anti-TPO confirms the underlying cause is autoimmune (not iodine deficiency, post-partum, post-viral, or drug-induced) and predicts that subclinical thyroid dysfunction is likely to progress.
This test is also clinically useful in pregnancy. Anti-TPO positive women have a much higher risk of post-partum thyroiditis (up to 50%) and miscarriage, so endocrinologists often retest TSH more frequently in this group. In families with strong autoimmune thyroid history, a positive anti-TPO in an asymptomatic relative warrants regular TSH monitoring.
How to prepare
No fasting required. Antibody levels are stable across the day and not affected by food or recent medication. Continue thyroid medication (levothyroxine, carbimazole) as usual — these do not alter antibody titres meaningfully.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Anti-Microsomal Antibody (Anti-TPO) (IU/mL)[1][2][3] | Negative: < 35 (assay-dependent — typical cut-offs 9–60 IU/mL) | Negative result makes autoimmune thyroid disease less likely but does not rule it out. About 5–10% of Hashimoto's patients are anti-TPO negative — anti-thyroglobulin (anti-Tg) antibody is sometimes positive in these cases. | Positive (often 100s to 1000s IU/mL) confirms autoimmune thyroid disease. The absolute level does not closely track disease activity and does not need repeat monitoring. Higher titres do predict faster progression to overt hypothyroidism in subclinical cases. |
Thyroid antibodies: which test for which condition
| Antibody | Disease | Positive in |
|---|---|---|
| Anti-TPO (anti-microsomal) | Hashimoto thyroiditis, Graves disease | 90% Hashimoto, 75% Graves |
| Anti-Thyroglobulin (anti-Tg) | Hashimoto thyroiditis | 60–80% Hashimoto |
| TSH Receptor Antibody (TRAb / TSI) | Graves disease | >95% active Graves |
| Combined Anti-TPO + Anti-Tg | Hashimoto thyroiditis | ~99% Hashimoto |
Frequently asked questions
Is AMA the same as anti-TPO?
In modern Indian labs, yes. The "microsomal" antigen targeted by AMA testing was later identified as thyroid peroxidase (TPO), so anti-TPO is the current term. Some labs still use the legacy name AMA.
Do I need fasting?
No. The test can be done at any time.
My TSH is normal but anti-TPO is positive — what does that mean?
You have autoimmune thyroiditis with currently normal thyroid function. Many people stay in this state for years. The risk of developing overt hypothyroidism is about 2–4% per year, so doctors usually recheck TSH every 6–12 months.
Will treating my thyroid lower the antibody level?
Not usually. Levothyroxine replaces missing hormone but does not stop the autoimmune process. Antibody titres typically remain elevated for years. They are not used to track treatment response — TSH is.
Should my children be tested?
If you have autoimmune thyroid disease, first-degree relatives are at higher risk. Children with symptoms (poor growth, fatigue) should have TSH and anti-TPO. Asymptomatic adult relatives can have TSH checked every few years.
Is anti-TPO important in pregnancy?
Yes. Anti-TPO positive women have higher rates of miscarriage and post-partum thyroiditis. Obstetricians monitor TSH more closely (every 4–6 weeks) and may start treatment earlier in pregnancy.
How quickly is the report ready?
Most Indian NABL-accredited labs report anti-TPO within 24 hours.
Related Autoimmune / Rheumatology tests
Tests commonly ordered alongside ANTI MICROSOMAL ANTIBODY (AMA), or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Thyroid Antibodies · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Hashimoto Thyroiditis · accessed 2026-05-30T00:00:00.000Z
- American Thyroid Association — Hashimoto Thyroiditis · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Thyroid Peroxidase Antibodies · accessed 2026-05-30T00:00:00.000Z
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