anti thyroid antibodies in thyroid .pptx

anti thyroid antibodies

1. Dr.Tittu Oommen Anti thyroid antibodies

2. The diagnostic hallmark of the autoimmune thyroid disorders is the presence, in most patients, of circulating antibodies and reactive T cells against one or another thyroid antigen. The most clinically relevant anti-thyroid autoantibodies are: Anti-thyroid peroxidase antibodies (anti-TPO antibodies) Thyrotropin receptor antibodies ( TRAbs ) Thyroglobulin antibodies.

3. At all ages, these antibodies are almost five times more common in women than in men. Selected groups at risk include younger women and relatives of patients with an autoimmune thyroid disorder, in whom the incidence is higher. The higher the concentration of autoantibody, the greater the clinical specificity. Tg-Ab and TPO- Ab are more common in patients with sporadic goiter , multinodular goiter , or isolated thyroid nodules and cancer than in the general population.

4. Thyroglobulin ( Tg ) & Anti- Tg

5. Thyroglobulin ( Tg ), the precursor protein for thyroid hormone synthesis, is detectable in the serum of most normal individuals when a sensitive method is used. The serum Tg level integrates three major factors: ( i ) the mass of differentiated thyroid tissue present (ii) any inflammation or injury to the thyroid gland which causes the release of Tg (iii) the amount of stimulation of the TSH receptor (by TSH, hCG or TRAb ).

6. Tg is normally detected in the circulation in concentrations between 3 and 40 ng / mL. When TSH is within the reference interval, each gram of thyroid tissue provides approximately 1 ng / mL of Tg to the circulation. At TSH concentrations less than 0.1 mIU /L, each gram of thyroid tissue releases only about 0.5 ng / dL of Tg into the plasma.

7. An elevated serum Tg concentration is a non-specific indicator of thyroid dysfunction. Elevated Tg concentrations can be seen in Goiter or thyroid neoplasia Trauma to the thyroid gland Inflammation (such as subacute thyroiditis or amiodarone -induced thyroiditis ) Surgical removal, or irradiation. Tg is typically decreased in Acquired hypothyroidism Congenital hypothyroidism (from thyroid hypoplasia ) Factitious hyperthyroidism (because of TSH suppression) Following thyroidectomy .

8. Uses of Tg The primary use of serum Tg measurements is as a tumor marker for patients carrying a diagnosis of differentiated thyroid cancer (DTC). After total thyroid ablation for papillary or follicular thyroid carcinoma, Tg should not be detectable, and its subsequent appearance signifies the presence of persistent disease. The serum Tg level is related to the volume of neoplastic tissue and may be undetectable in patients with small lymph node metastases that can be detected on neck ultrasonography .(current guidelines recommend combination of Tg and anatomic imaging for post operative monitoring of DTC.)

9. Single rhTSH -stimulated serumTg <0.5 ng / mL in the absence of anti- Tg antibody has an approximately 98–99.5% likelihood of identifying patients completely free of tumor on follow-up* There is good evidence that a Tg cutoff level above 2 ng / mL following rhTSH stimulation is highly sensitive in identifying patients with persistent tumor * * Revised American Thyroid Association Management Guidelines for Patients with Thyroid Nodules and Differentiated Thyroid Cancer-2009

10. Serum Tg should be measured every 6–12 months by an immunometric assay . Ideally, serum Tg should be assessed in the same laboratory and using the same assay. Thyroglobulin antibodies should be quantitatively assessed with every measurement of serum Tg . The results can be artifactually altered by serum anti- Tg antibodies ( Tg-Ab ), and serum should be screened for Tg-Ab with a sensitive immunoassay. Interferences lead to underestimations of Tg or false-negative values.

11. Differentiated Thyroid Cancer and Positive Anti- Thyroglobulin Antibodies The frequency of antibodies is approximately 20–25%. Higher than the approximately 10% frequency reported in the general population. The eventual disappearance of Tg antibodies takes approximately 2–3 years on average. The difference in antibody prevalence in DTC populations may in part be related to the use of different anti- Tg antibody assays or Differences in the frequency of lymphocytic thyroiditis . Anti- Tg antibodies tend to cause an underestimation of Tg when IMA is used, whereas they can cause either an under- or overestimation of RIA measurements.

12. Discordant results between different assays may be minimized by using: Lower limit of detection, rather than the lower part of the normal range to define the presence of anti- Tg antibodies. To repeat the measurements using a different method(in case of heterogenous epitopes ) Studies suggest that neck ultrasound, perhaps in combination with other imaging based on risk of metastatic disease determined by risk features of individual patients, should be performed in an effort to identify disease in patients with persistent or rising anti- Tg antibodies.

13. Serum Tg Measurement for Non- Neoplastic Conditions For diagnosing thyrotoxicosis factitia which is characterized by a non-elevated serum Tg . To investigate the etiology of congenital hypothyroidism in infants detected by neonatal screening. To assess the activity of inflammatory thyroiditis , eg subacute thyroiditis , or amiodarone -induced thyroiditis . Provides a good marker of iodine status in the population.

14. Antithyroid peroxidase antibodies (Anti TPO) Anti-thyroid peroxidase (anti-TPO) antibodies are specific for the autoantigen TPO, a 105kDa glycoprotein that catalyses iodine oxidation and thyroglobulin tyrosyl iodination reactions in the thyroid gland Anti-TPO antibodies are the most common anti-thyroid autoantibody.

15. Appear to be a secondary response to thyroid injury and are not thought to cause disease themselves, although they may contribute to its development and chronicity . TPO- Ab on the surface of B cells may be involved in antigen presentation, thus activating thyroid-specific T cells.

16. The disease most widely associated with TPO- Ab is autoimmune thyroiditis , or Hashimoto’s disease. Also detectable in 50% to 90% of patients with Graves’ disease - Testing for TSHR antibodies remains the test of choice in such patients. More common in patients with sporadic goiter , multinodular goiter , or isolated thyroid nodules and cancer than in the general population. This finding usually represents an associated thyroiditis on histologic examination.

17. At all ages, these antibodies are almost five times more common in women than in men. High levels remain a significant risk factor in families with autoimmune thyroid disorders.

18. Thank you