Unit Converter
Antibody to thyroglobulin (anti-Tg)
(Thyroglobulin Antibody – TgAb – Autoimmune Thyroid Disease Marker)
Synonyms
- Anti-Tg
- Thyroglobulin antibody
- TgAb
- Anti-thyroglobulin antibody
- Autoantibody to thyroglobulin
Units of Measurement
- IU/mL
- kIU/L
(Both units are numerically equivalent: 1 IU/mL = 1 kIU/L)
Description
Anti-Tg antibodies are autoantibodies directed against thyroglobulin, the large glycoprotein precursor used by the thyroid gland to produce T3 and T4.
Anti-Tg is useful for:
- Diagnosing autoimmune thyroid disease
- Interfering with thyroglobulin tumor marker assays
- Monitoring differentiated thyroid cancer (DTC) patients
- Predicting risk of hypothyroidism in euthyroid individuals
Anti-Tg antibodies often coexist with Anti-TPO antibodies, especially in Hashimoto thyroiditis.
Physiological Background
Thyroglobulin is synthesized in thyroid follicular cells and stored in the colloid.
Autoantibodies appear when:
- Follicular cell damage exposes Tg
- Autoimmune activation occurs (T helper 1/Th17 mediated)
Anti-Tg antibodies can:
- Interfere with Tg measurement
- Mark ongoing autoimmune destruction
Clinical Significance
Elevated Anti-Tg
1. Hashimoto Thyroiditis
- Positive in 60–80% of patients
- Usually accompanied by Anti-TPO
- Predicts progression to hypothyroidism
2. Graves Disease
- Positive in 30–50%
- Not as specific as Anti-TSHR or Anti-TPO
3. Differentiated Thyroid Cancer (DTC) Monitoring
Anti-Tg presence interferes with thyroglobulin measurement (Tg becomes unreliable).
Thus:
- Falling Anti-Tg → good prognosis
- Rising Anti-Tg → recurrence risk
- Used when Tg cannot be interpreted due to antibody interference
4. Other Autoimmune & Systemic Diseases
Low-level positivity may occur in:
- Type 1 diabetes
- Pernicious anemia
- Celiac disease
- Sjögren syndrome
- SLE
5. Pregnancy
Positive anti-Tg in early pregnancy increases risk of:
- Miscarriage
- Postpartum thyroiditis
- Future hypothyroidism
Low or Negative Anti-Tg
- Does not rule out autoimmune thyroid disease.
- Anti-TPO is more sensitive for Hashimoto thyroiditis.
Reference Intervals
Typical Cutoffs
| Anti-Tg Level | Interpretation |
| < 4 IU/mL | Negative |
| 4–10 IU/mL | Borderline / weak positive |
| > 10 IU/mL | Positive |
| > 100–500 IU/mL | Strong autoimmune activity |
| Very high (>1000 IU/mL) | Often in active Hashimoto thyroiditis |
In Thyroid Cancer Follow-up
- Anti-Tg presence invalidates Tg measurement
- Trends (up/down) are more important than absolute numbers
Diagnostic Uses
1. Autoimmune Thyroiditis
Used along with:
- Anti-TPO
- TSH
- Ultrasound (heterogeneous, hypoechoic gland)
2. Thyroid Cancer Follow-Up
In patients with differentiated thyroid cancer:
- Anti-Tg interferes with Tg → use Anti-Tg trend
- Falling titers suggest successful ablation
- Rising titers indicate recurrence/metastasis
3. Pregnancy Thyroid Screening
Anti-Tg positivity increases risk for:
- Postpartum thyroiditis
- Hypothyroidism
- Pregnancy loss
4. Euthyroid Individuals with Positive Antibodies
Predict long-term risk of hypothyroidism
→ Monitor TSH annually.
Analytical Notes
- Test via chemiluminescent immunoassay or ELISA.
- Anti-Tg can significantly interfere with serum thyroglobulin (Tg) assays.
- Always report Tg and Anti-Tg together in thyroid cancer surveillance.
- Biotin supplementation may cause assay interference—stop 48 hrs before test.
- Consider method consistency for serial monitoring.
Clinical Pearls
- Anti-Tg alone is less sensitive than Anti-TPO for Hashimoto thyroiditis.
- Presence of Anti-Tg makes thyroglobulin unreliable as a tumor marker.
- In thyroid cancer: rising Anti-Tg after surgery = concern for recurrence.
- Anti-Tg is important even if thyroid function tests (TSH, FT4) are normal.
- High Anti-Tg during pregnancy predicts postpartum thyroid dysfunction.
Interesting Fact
Anti-Tg was one of the first thyroid autoantibodies discovered (1956), long before the identification of Anti-TPO and Anti-TSHR.
References
- Tietz Clinical Chemistry and Molecular Diagnostics, 8th Edition - Thyroid Autoantibodies.
- American Thyroid Association (ATA) 2015/2016 Guidelines.
- ESAP Endocrine Society - Autoimmune Thyroiditis Interpretation.
- Mayo Clinic Laboratories - Thyroglobulin Antibody Test.
- ARUP Consult - Thyroiditis & Thyroid Cancer Monitoring.
- IFCC Immunoassay Standards.
- NIH / MedlinePlus - Anti-Tg Overview.