Summary
Thyroglobulin Antibodies (TG Ab) target thyroglobulin — the large storage protein inside the thyroid gland from which T3 and T4 are assembled. Elevated TG Ab is found in Hashimoto's thyroiditis and Graves' disease, and is always tested alongside TPO Ab to maximise diagnostic sensitivity for autoimmune thyroid disease.
TG Ab is particularly valuable when TPO Ab is negative but autoimmune thyroid disease is still suspected. Around 10% of people with Hashimoto’s test positive for TG Ab but not TPO Ab, making TG Ab an essential diagnostic complement.
In patients treated for differentiated thyroid cancer, TG Ab is a critical interference marker. It can falsely suppress thyroglobulin (Tg) measurements used to monitor for cancer recurrence — making TG Ab an indispensable companion test in post-thyroidectomy monitoring.
What It Is
Thyroglobulin (Tg) is a large glycoprotein produced exclusively by the thyroid gland. It serves as the scaffold on which T3 and T4 are assembled and stored within thyroid follicles. When stimulated by TSH, the thyroid cleaves and releases thyroid hormones from thyroglobulin into the bloodstream.
In autoimmune thyroid disease, the immune system generates antibodies against thyroglobulin. These TG Ab reflect ongoing autoimmune attack on the thyroid and can be detectable years before clinical dysfunction develops.
TG Ab is less sensitive than TPO Ab for Hashimoto’s overall, but adds meaningful value by identifying the ~10% of autoimmune cases that are TPO Ab negative.
Functions
Autoimmune activity marker
Signals ongoing immune attack on the thyroid, complementing TPO Ab for a complete autoimmune picture.
Diagnostic gap filler
Identifies the ~10% of Hashimoto's cases that are TPO Ab negative but TG Ab positive.
Cancer monitoring adjunct
Must be measured alongside thyroglobulin in post-thyroidectomy patients to detect assay interference that could mask recurrence.
Disease activity monitor
Serial TG Ab measurements help track autoimmune activity and response to therapeutic interventions over time.
Reference Ranges
Serum Thyroglobulin Antibodies
Measured in IU/mL| Status | Range (IU/mL) | What it means |
|---|---|---|
| Negative | < 115 | No significant thyroglobulin autoimmunity detected. |
| Borderline | 115–200 | Low-level antibodies — monitor annually with full thyroid function and TPO Ab. |
| Elevated | > 200 | Significant thyroid autoimmunity — consistent with Hashimoto's or Graves' disease. |
TG Ab ranges vary between assays. Titres alone do not predict the rate of thyroid function loss — interpret alongside TSH, Free T4, and TPO Ab.
Symptoms of Imbalance
Symptoms from elevated TG Ab are those caused by the autoimmune thyroid disease it reflects.
- No symptoms from a negative TG Ab result — absence of thyroglobulin autoimmunity is normal
- Fatigue and low energy from associated thyroid dysfunction
- Neck swelling or discomfort (goitre)
- Fluctuating thyroid symptoms in early Hashimoto's
- Brain fog and mood disturbance
- Cold intolerance and weight changes if hypothyroidism develops
- Recurrent miscarriage in women of reproductive age
- Mild generalised aches from autoimmune inflammation
Causes of Imbalance
- No pathological cause — a negative result is expected and normal
- Hashimoto's thyroiditis
- Graves' disease
- Other autoimmune conditions (lupus, rheumatoid arthritis, coeliac disease)
- Family history of autoimmune thyroid disorders
- History of thyroid cancer treatment (post-thyroidectomy)
- Postpartum thyroiditis
FAQs
Both are autoimmune thyroid antibodies. TPO Ab targets the enzyme that makes thyroid hormones and is positive in ~95% of Hashimoto’s cases. TG Ab targets the protein that stores thyroid hormones and is positive in ~60% of cases. Testing both together maximises sensitivity — a small but significant group are TG Ab positive but TPO Ab negative.
Not immediately, but it warrants monitoring. Elevated TG Ab with normal TSH and Free T4 means your immune system is targeting the thyroid but the gland is still producing sufficient hormone. Annual thyroid function testing is recommended, as ~5% of people with positive thyroid antibodies progress to overt hypothyroidism per year.
After thyroidectomy, thyroglobulin (Tg) levels are used to detect cancer recurrence — any detectable Tg suggests residual cancer. However, TG Ab can bind thyroglobulin in the test tube and falsely suppress the Tg result, masking recurrence. TG Ab must always be measured simultaneously with Tg to determine whether the result is reliable.
Yes. TG Ab titres can decrease naturally, particularly in patients with stable euthyroid function on levothyroxine. Selenium supplementation may also modestly reduce autoimmune antibody levels. Fluctuation in antibody levels is common and not always clinically significant.
No. Approximately 5–10% of people with confirmed Hashimoto’s are seronegative for both TPO Ab and TG Ab. In these cases, thyroid ultrasound showing the characteristic heterogeneous, hypoechoic appearance provides important additional evidence alongside clinical symptoms.
References
- Caturegli P, et al. Hashimoto's thyroiditis: clinical and diagnostic criteria. Autoimmun Rev. 2014;13(4–5):391–397. View source
- Spencer CA. Thyroglobulin in thyroid cancer. Thyroid. 2011;21(12):1361–1365. View source
- Latrofa F, et al. Thyroglobulin autoantibodies. Best Pract Res Clin Endocrinol Metab. 2020;34(1):101372. View source