.
Less than 20 IU/mL (<20 IU/mL)
Uncertainty of measurement = 12%
.
There are two main autoimmune thyroid diseases; Grave's (hyperthyroidism) and Hashimoto's (hypothyroidism). Primary myxedema is often included, which is a subset of autoimmune thyroid disease.
Grave's disease accounts for approximately 60% of all hyperthyroid cases and has a case frequency in the order of five times biased towards females. Symptoms include over-excitability, heat intolerance, sleep / concentration problems. Endocrine-based eye problems occur in approximately 40% of cases. Relapse is common, but spontaneous remission can occur as can a change to hypothyroidism.
Hashimoto's disease has a slow and insidious onset. Like Grave's, it's frequency is biased towards women (5-20 times over males). The disease is characterised by weight gain, muscle weakness, cold skin and nail brittleness. Hashimoto's disease is usually found in conjunction with other autoimmune disorders, in particular, myasthenia gravis, pernicious anaemia and atrophic gastritis.
Clinical features of primary myxedema are not unlike those of Hashimoto's. Additional features include voice deepening, skin swelling and eyelid droop. Cardiac tissue may be infiltrated leading to cardiac myxedema.
There are two commercially available assays (anti-thyroglobulin and anti-thyroid peroxidase) for autoimmune thyroiditis. Thyroglobulin is a large MW protein located in the colloid of the thyroid follicle. It is the substratum for the synthesis of the thyroid hormones T4 (thyroxine) and T3 (3-5-3' triidothyronine). Thyroid peroxidase is the dominant enzyme involved in T4 and T3 synthesis.
Thyroid antibodies play an important role in excluding autoimmune thyroiditis, as over 98% of patients with autoimmune-based thyroiditis will have antibodies to thyroglobulin, thyroid peroxidase or both. As can be seen from the following table, anti-thyroglobulin not only has a very poor positive predictive value in Grave's disease, it is also found in cases of adenosarcoma, non-autoimmune thyroiditis and in approximately 10% of healthy individuals at low titre.
A high level of antibody may predict future thyroid dysfunction and the patient should have thyroid tests undertaken every 6-12 months or earlier if symptoms develop.
|
Disease |
Anti-TPO |
Anti-Tg |
|
Grave's |
71-97% |
30% |
|
Hashimoto's |
91-99% |
85% |
In Hashimoto's disease, the histologic severity is positively correlated with TPO antibody level.
Reference
Hyperthyroidism and other causes of thyrotoxicosis: Management Guidelines of the American Thyroid Association and the American Association of Clinical Endocrinologists. Thyroid 2011; 6: 593-646
For further information contact the laboratory, (09) 307 4949 ext 22103 or:
Associate Professor Rohan Ameratunga
, Immunopathologist: Locator
93-5724,
If there is a >24h delay in sending specimens (whole blood or separated serum) retain at 4 o C