Anti-TPO Antibodies
Anti-TPO· also: TPOAb, Anti-thyroid peroxidase
Clinical Overview
Anti-thyroid peroxidase (Anti-TPO) antibodies are autoantibodies that attack thyroid peroxidase, an enzyme essential for thyroid hormone synthesis. They are the most common thyroid autoantibodies and are the primary marker of autoimmune thyroid disease — particularly Hashimoto's thyroiditis and Graves' disease.
Why This Test Matters
Anti-TPO antibodies are positive in >90% of Hashimoto's thyroiditis and 70–80% of Graves' disease. Their presence predicts progression from subclinical hypothyroidism to overt hypothyroidism and from euthyroidism to hypothyroidism over time. In pregnant women with anti-TPO antibodies, the risk of postpartum thyroiditis and fetal thyroid dysfunction is significantly increased. Measurement is indicated in any patient with unexplained TSH abnormality.
Reference RangesWHO/IFCC standards
| Reference Range | Unit | Notes |
|---|---|---|
| 0 – 34 | IU/mL | Negative <34 |
Also reported in: kIU/L.
What Causes Abnormal Results?
High Anti-TPO Causes
- Hashimoto's thyroiditis (most common)
- Graves' disease
- Postpartum thyroiditis
- De Quervain's (subacute) thyroiditis
- Other autoimmune conditions: type 1 diabetes, rheumatoid arthritis, SLE
- Low-level positivity in up to 15% of healthy women
Low Anti-TPO Causes
- Not clinically applicable (negative is normal)
Signs & Symptoms to Watch For
How to Prepare for This Test
No special preparation required.
Factors That Can Affect Results
- Low-level positivity is common in healthy women (especially elderly)
- Anti-TPO titers do not correlate with disease severity
Related Topics
Frequently Asked Questions
If anti-TPO is positive but TSH is normal, do I need treatment?
No immediate treatment is needed if TSH is normal. Positive anti-TPO antibodies with normal TSH is called euthyroid Hashimoto's. However, these patients should have annual TSH monitoring because the risk of developing hypothyroidism is 2–4% per year. Treatment with levothyroxine is reserved for when TSH rises above the normal range, or in certain clinical contexts like pregnancy planning.
Does a high anti-TPO level mean more severe thyroid disease?
Not necessarily. The level of anti-TPO antibodies does not reliably predict disease severity or the speed of progression to hypothyroidism. A very high titer may signal more active autoimmune inflammation, but clinical management (when to treat) is based on TSH and FT4 levels, not on anti-TPO levels alone.