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Introduction ⬇

There are several autoantibodies that are organ specific for the thyroid gland, but antithyroglobulin and antithyroperoxidase are ordered most frequently by healthcare providers when evaluating patients for hyperthyroidism, hypothyroidism, and thyroid cancer. With Graves disease, which is autoimmune hyperthyroidism, and with Hashimoto thyroiditis, which is autoimmune hypothyroidism, the presence of both antibodies can help confirm the diagnosis.

Thyroglobulin antibodies are directed against the glycoprotein thyroglobulin located in the thyroid follicles; thyroperoxidase (TPO) antibodies are directed against the membrane-bound glycoprotein TPO located in the cytoplasm of the epithelial cells surrounding the follicles.

Along with chemiluminescence technology, highly purified antigens have been used to improve specificity. For the antithyroperoxidase test, instead of using the entire microsomal antigen, this assay uses just the TPO component. TPO is considered the primary autoantigenic component of the microsomal antigen. Test systems that use the purified TPO (in place of the microsomal antigen) have greater specificity for the clinically significant autoantibody. Assays using microsomal antigen are detecting TPO antibody but may also detect antibodies to other parts of the microsomal antigen that have little or no clinical significance.

Normal Findings ⬆ ⬇

Procedure ⬆ ⬇

  1. Collect 7-mL blood serum in a red-topped tube. Observe standard precautions.

  2. Label the specimen with the patient’s name, date, and test(s) ordered and place in a biohazard bag for transport to the laboratory.

Clinical Implications ⬆ ⬇

  1. High titers of thyroglobulin and thyroid microsomal antibodies (>1:400) are found with Hashimoto disease, but elevations can also be seen in other autoimmune diseases.

  2. Increased thyroid antibodies also occur in the following conditions:

    1. Graves disease

    2. Thyroid carcinoma

    3. Idiopathic myxedema

    4. Pernicious anemia

    5. SLE, RA, Sjögren syndrome

    6. Subacute thyroiditis

    7. Nontoxic nodular goiter

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure. Thyroid antibody testing is done to confirm diagnosis. It is not to be relied on, however, for management of the disease.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing. The diagnosis of autoimmune thyroiditis is made on the basis of clinical observations, thyroid function tests (see Chapter 6), and the presence of circulating autoantibodies, such as thyroglobulin and microsomal (TPO).

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. About 10% of the normal population may have low levels of thyroid antibodies with no symptoms of the disease. Incidence of low titer is higher in women and increases with age.

  2. Antibody production may be confined to lymphocytes within the thyroid, resulting in negative serum test results.