Antibodies, Antithyroglobulin, and Antithyroid Peroxidase

Synonym/acronym: Thyroid antibodies, antithyroid peroxidase antibodies (thyroid peroxidase [TPO] antibodies were previously called thyroid antimicrosomal antibodies).

Common use

To assist in diagnosing hypothyroid and hyperthyroid disease.

Specimen

Serum (1 mL) collected in a red-top tube.

Normal findings

(Method: Immunoassay)

Antibody	Conventional Units
Antithyroglobulin antibody	Less than 20 international units/mL
Antiperoxidase antibody
Newborn–3 days	0–9 international units/mL
4–30 days	0–26 international units/mL
1–12 mo	0–13 international units/mL
13 mo–19 yr	0–20 international units/mL
20 yr–older adult	0–34 international units/mL

Description

Thyroid peroxidase (TPO) is a key enzyme in the formation of thyroid hormones and thyroglobulin is the stored precursor to the active, iodinated thyroid hormones. Antibodies to both may form and affect normal thyroid function. Both tests are normally requested together. Thyroid antibodies are mainly immunoglobulin G–type antibodies. Antithyroid peroxidase antibodies (anti-TPO antibodies) bind with microsomal antigens on cells lining the microsomal membrane of thyroid tissue. They are thought to destroy thyroid tissue as a result of stimulation by lymphocytic killer cells. These antibodies are present in hypothyroid and hyperthyroid conditions. Anti-TPO antibodies are present in Hashimoto’s autoimmune thyroiditis, a major cause of hypothyroidism. Hypothyroidism in women of childbearing age is a significant concern because of the deleterious effects of insufficient thyroxine levels on fetal brain development. Anti-TPO antibodies are also demonstrable in Graves’ disease, a major cause of hyperthyroidism. Graves’ disease is the most common type of thyrotoxicosis in women of childbearing age, impairing fertility and increasing risk of miscarriage to 26%. Transplacental passage of anti-TPO antibodies in pregnant patients may affect the developing fetus or lead to thyroid disease in the neonate. Mild depression is more common in postpartum women with anti-TPO antibodies.

This procedure is contraindicated for

N/A

Indications

Assist in confirming suspected inflammation of thyroid gland
Assist in the diagnosis of suspected hypothyroidism caused by thyroid tissue destruction
Assist in the diagnosis of suspected thyroid autoimmunity in patients with other autoimmune disorders

Potential diagnosis

Increased in

The presence of these antibodies differentiates the autoimmune origin of these disorders from non-autoimmune causes, which may influence treatment decisions.
Autoimmune disorders
Graves’ disease
Goiter
Hashimoto’s thyroiditis
Idiopathic myxedema
Pernicious anemia
Thyroid carcinoma

Decreased in

N/A

Critical findings

N/A

Interfering factors

Lithium may increase thyroid antibody levels.

Nursing Implications and Procedure

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient this test can assist in evaluating thyroid gland function.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
Obtain a history of the patient’s endocrine and immune systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
Note any recent procedures that can interfere with test results.
Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
Note that there are no food, fluid, or medication restrictions unless by medical direction.

Intratest

Potential complications: N/A
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
Promptly transport the specimen to the laboratory for processing and analysis.

Post-Test

Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

Related tests include biopsy thyroid, CBC, FT₃, FT₄, RAIU, T4, thyroid scan, thyroglobulin, TSH, TT3, and US thyroid.
See the Endocrine and Immune systems tables at the end of the book for related tests by body system.