Anti-thyroglobulin antibody

Sample

1. Collect 3 to 5 ml of blood and prepare serum.
2. Keep the serum frozen if the test is not done on the same day.
3. The fasting sample is preferred.

Precautions

1. Stop multivitamins and any other medication which will interfere with the result.
2. Oral contraceptives may increase their value.
3. Older people, especially women, may have antithyroglobulin antibodies.

Purpose of the test (Indications)

1. Useful for diagnosing thyroid diseases like Hashimoto’s thyroiditis and chronic lymphocytic thyroiditis.
2. It differentiates Hashimoto’s thyroiditis and chronic lymphocytic thyroiditis.

Pathophysiology of Anti-thyroglobulin autoantibody:

1. Several autoantibodies are organ-specific for the thyroid gland.
2. The possible thyroid antigens giving rise to antibodies are:
   1.  Hormone antigen.
   2. Thyroglobulin antigen.
   3. Thyroid microsomal antigen.
   4. Thyroid peroxidase antigen
   5. TSH-R antigen.
   6. Non-thyroglobulin colloidal antigen.
   7. Rarely can measure:
      1. TSH antigen.
      2. T4 and T3 antigen
   8. Out of these

3. Mostly anti-thyroglobulin and anti-thyroperoxidase are more frequently ordered by the physician.
4. These are advised to evaluate:
   1. Hypothyroidism.
   2. Hyperthyroidism.
   3. Thyroid malignancies.
   4. In Grave’s disease (autoimmune hyperthyroidism).
   5. In Hashimoto’s thyroiditis (autoimmune hypothyroidism).
5. This is an autoimmune phenomenon. There is the formation of autoantibody against thyroglobulin called the anti-thyroglobulin antibody.
   1. Thyroperoxidase is mostly used for autoimmune thyroid diseases.

Thyroglobulin:

1. It is a glycoprotein, 660 kD, a dimeric protein produced by the follicular cells and is used entirely in the gland.
2. This is the precursor of the thyroid hormone (thyroxine and triiodothyronine).
   1. Thyroglobulin combines with T4 by oxidation through peptide linkage.
3. Thyroglobulin is synthesized in the follicular cells.
   1. There is a high concentration of thyroglobulin in the colloid inside the thyroid follicle.
   2. It enters the lumen of the follicle by the process of exocytosis.
4. The thyroglobulin located in the thyroid follicle can escape the follicle and becomes an antigen.
   1. Thyroperoxidase is located in the cytoplasm of the epithelial cells surrounding the follicles.
5. Circulating thyroglobulin’s half-life is about 65 hours.
   1. It takes nearly a month before thyroglobulin becomes undetectable after the total thyroidectomy.
   2. Thyroglobulin is a demo cleared from the blood circulation by the catabolism in the liver and recycling in the thyroid.

Anti-thyroglobulin antibody: Thyroglobulin role in T3 T4 and autoantibody formation

Autoantibodies against thyroglobulin:

1. These autoantibody reacts with thyroglobulin and leads to thyroid destruction and inflammation.
2. Anti-thyroglobulin antibodies are present in 10% of the normal population and >20% in thyroid cancer.
3. An increase in the anti-thyroglobulin antibody indicates antigenic stimulation, suggesting recurrence.
4. If these antibodies are present in the mother, there is an increased risk of hypo or hyperthyroidism in the fetus and the newborn.

5. Other thyroid autoantibodies form against microcosms and are called anti-microsomal antibodies; these are also advised to diagnose thyroid diseases.
   1. The most commonly advised antibodies are thyroid peroxidase autoantibodies.
6. A high titer of anti-thyroglobulin and anti-microsomal antibodies level of  >1:400 is found in Hashimoto’s thyroiditis.
   1. Thyroglobulin can be used as a tumor marker.
      1. 2/3 of the patient with thyroid cancer have raised their level of thyroglobulin.
      2. Anti-thyroglobulin antibodies can also be used to monitor the residual disease or to find the recurrence.
      3. An increased level of the Anti-Thyroglobulin indicates the recurrence of the disease (cancer).

Table showing % of the antithyroglobulin antibodies in various diseases.

 When to ask for an antithyroglobulin antibody test (Clinical presentation):

1. If the patient has the following symptoms:
   1. If there is weight gain without any explanation.
   2. Patients have a history of fatigue.
   3. History of constipation.
   4. In the case of dry skin.

The normal level of  antithyroglobulin antibody:

Source 2

• Negative = Titer = <1:100
  • A small normal population may have an antithyroglobulin antibody.
  • 5 to 10% normal population may show low titer.

Source 4

1. Anti-thyroglobulin = <1:100 (by haemagglutination).
2. Negative by ELIZA.
3. Negative by chemiluminescence.
   1. 10% of the population have low titer positive for the antibody without any symptoms of thyroid disease.
      1. This low titer is common in women and the increasing age.
4. In some cases, this antibody production may be confined to the lymphocytes within the thyroid, resulting in negative serum tests.

How to measure anti-thyroglobulin antibody:

There are different methods to detect anti-thyroglobulin antibodies like:

1. Passive hemagglutination.
2. The agar gel diffusion precipitation method.
3. Immunofluorescence of the tissue biopsy.
4. Enzyme-linked Immunoabsorbent assay (ELIZA).
5. Chemilucent-based immunoassay.

The increased Anti-thyroglobulin antibody level is seen in:

1. Chronic thyroiditis like Hashimoto thyroiditis in the adult.
   1. The titer is high >1:25,000 is strongly suggestive of Hashimoto’s disease.
   2. This autoantibody is positive in 50% of the cases of Hashimoto’s thyroiditis.
   3. The normal level of thyroglobulin antibody does not rule out Hashimoto’s disease.
2. Chronic lymphocytic thyroiditis in children and young adults.
3. Graves’ disease.
4. Hypothyroidism.
5. Atrophic thyroiditis.
6. Thyroid cancer
7. Thyrotoxicosis.
8. Myxedema.
9. Pernicious anemia.
10. Sjogren’s syndrome.
11. Lupus erythematosus.

• Table showing various thyroid diseases and autoantibodies:

• LATS consists of two antibodies:
  • TSI = Thyroid stimulating immunoglobulin.
  • TSH-R antibody = Thyroid hormone receptor antibody.

Questions and answers: