Overview
The Anti-Thyroglobulin Antibody (ATG) test is a blood test that helps detect antibodies that attack a protein called thyroglobulin, which is naturally produced in the thyroid gland. Thyroglobulin is an essential protein used by the thyroid to make thyroid hormones (T3 and T4).
In a healthy person, the immune system protects the body from infections and foreign invaders. However, in some cases, the immune system mistakenly identifies the body’s own thyroid tissues as harmful and starts producing antibodies against them — this condition is known as an autoimmune thyroid disease.
When anti-thyroglobulin antibodies are present in the blood, it usually indicates that the immune system is attacking the thyroid gland. This can cause thyroid inflammation or dysfunction, leading to disorders such as Hashimoto’s thyroiditis or Graves’ disease.
What is the Anti-Thyroglobulin Antibody (ATG) Test?
The ATG test measures the level of antibodies against thyroglobulin in your blood. These antibodies are a type of autoantibody, meaning they are produced by your immune system against your own body’s proteins.
If the test detects ATG antibodies, it suggests that the immune system is reacting abnormally to thyroid tissues, possibly leading to thyroid damage, inflammation, or hormone imbalance.
Main Uses of the ATG Test:
- To diagnose autoimmune thyroid diseases like Hashimoto’s thyroiditis and Graves’ disease.
- To support the diagnosis of thyroid inflammation or dysfunction when thyroid hormone levels are abnormal.
- To monitor patients after thyroid cancer treatment, especially those who have had their thyroid gland removed.
This test is often ordered along with anti-thyroid peroxidase (TPO) antibodies, TSH, and thyroid hormone tests (T3 and T4) for a complete evaluation of thyroid health.
Where Are Anti-Thyroglobulin Antibodies Produced?
These antibodies are produced by B-cells, which are part of the body’s immune system.
In autoimmune thyroid diseases, B-cells mistakenly identify the thyroid protein thyroglobulin as a threat. In response, they start making anti-thyroglobulin antibodies (ATG) that attack and damage thyroid cells.
This abnormal immune reaction can cause inflammation, disrupt hormone production, and lead to either hypothyroidism (low thyroid activity) or hyperthyroidism (overactive thyroid) depending on the condition.
Functions and Importance of the ATG Test
Under normal circumstances, ATG antibodies should not be present in the bloodstream.
If the test shows positive for these antibodies, it suggests that the immune system is targeting the thyroid gland. This information helps doctors in several ways:
Importance of ATG Test:
- Helps diagnose autoimmune thyroid disorders, especially Hashimoto’s thyroiditis and Graves’ disease.
- Useful in monitoring thyroid cancer patients after surgery or radioactive iodine treatment.
- Aids in evaluating unexplained thyroid function abnormalities (e.g., abnormal TSH or hormone levels without a clear reason).
In thyroid cancer cases, ATG antibodies are monitored to ensure there’s no recurrence or residual thyroid tissue after treatment.
Causes of Low or Negative ATG Levels
A negative or low ATG level usually means there is no autoimmune activity against the thyroid gland.
Common Causes of Low/Negative ATG Levels:
- Normal thyroid function and no autoimmune response.
- Absence of autoimmune thyroid disease.
- Successful treatment and remission in thyroid cancer patients.
Symptoms of Low/Negative ATG Levels:
There are no symptoms when ATG levels are low or negative — this is a normal and healthy finding.
However, if thyroid-related symptoms (like fatigue, weight change, or mood swings) still persist, doctors may recommend additional tests such as TPO antibodies, TSH, and Free T4 to rule out other conditions.
Causes of High ATG Levels
A high level of anti-thyroglobulin antibodies indicates that your immune system is reacting against your thyroid gland. This may occur in various thyroid disorders.
Common Causes of High ATG Levels:
- Hashimoto’s thyroiditis – The most common autoimmune cause of high ATG. It gradually damages the thyroid and leads to hypothyroidism.
- Graves’ disease – Another autoimmune condition that overstimulates the thyroid, leading to hyperthyroidism.
- Thyroid cancer – Especially in papillary or follicular types.
- Post-thyroidectomy monitoring – After thyroid removal, rising ATG levels may indicate cancer recurrence.
- Other autoimmune disorders – Rarely, conditions like rheumatoid arthritis or lupus can show mildly elevated ATG levels.
Symptoms of High ATG Levels
ATG antibodies themselves do not cause symptoms. However, they are markers of thyroid disease — so symptoms depend on the underlying thyroid condition.
Common Symptoms Associated with High ATG Levels:
- Fatigue or weakness
- Weight gain (in hypothyroidism) or weight loss (in hyperthyroidism)
- Hair thinning or hair loss
- Dry, rough skin
- Irregular menstrual cycles
- Sensitivity to cold or heat
- Swelling or lump in the neck (goiter)
- Mood swings, anxiety, or depression
These symptoms occur because the thyroid gland directly influences your body’s metabolism, energy, and mood.
Reference Ranges for ATG Test
| Result | ATG Level (IU/mL) | Interpretation |
|---|---|---|
| < 20 IU/mL | Normal / Negative | No autoimmune activity |
| 20–115 IU/mL | Borderline / Mild elevation | Possible mild autoimmune response |
| > 115 IU/mL | Positive / Elevated | Active autoimmune thyroid disease or cancer |
⚠️ Note: Reference values may vary slightly depending on the laboratory and testing method used. Always interpret results with your doctor’s guidance.
Sample Requirements
- Sample Type: Serum (blood sample)
- Tube Type: Red Top (Plain Tube) or Serum Separator Tube
- Fasting: Not required
- Time of Collection: Can be done at any time of the day
The blood sample is collected from a vein in your arm, and the test results are usually available within 24–48 hours.
Test Preparation
- No fasting or special preparation is needed.
- Inform your doctor if you are taking thyroid medication, steroids, or supplements, as these can sometimes affect test interpretation.
- If you’ve had radioactive iodine therapy or thyroid surgery, your doctor may recommend this test regularly for follow-up monitoring.
When to Consult a Doctor
You should consult a doctor if you experience:
- Persistent fatigue, weight changes, or mood swings
- Swelling in the neck or signs of goiter
- Unexplained changes in body temperature tolerance (cold or heat sensitivity)
- Irregular menstrual cycles or fertility problems
- If you have a family history of thyroid or autoimmune disorders
A doctor may order the ATG test along with TPO antibodies, TSH, and Free T4 to get a complete picture of your thyroid health.
Important Word Explanations
- Thyroglobulin: A protein made by the thyroid gland used to produce thyroid hormones.
- Autoimmune Disease: A condition where the body’s immune system attacks its own tissues.
- B-cells: A type of white blood cell that produces antibodies.
- Thyroiditis: Inflammation of the thyroid gland.
- Hypothyroidism: Underactive thyroid producing too little hormone.
- Hyperthyroidism: Overactive thyroid producing too much hormone.
- Thyroidectomy: Surgical removal of the thyroid gland.
~END~