TPO Antibodies - Kresser Institute Membership Site

Marker Name: TPO antibodies

REFERENCE RANGES FOR SERUM TPO ANTIBODIES:

Laboratory reference range: 0–34 IU/mL

DESCRIPTION:

TPO stands for thyroid peroxidase, which is an enzyme that is integral to thyroid hormone synthesis in the thyroid gland.¹ Unfortunately, this enzyme can also become an antigen in autoimmune thyroid disease. The consequence of the ensuing autoimmune response is the production of antibodies directed against TPO. TPO antibodies detected in blood help determine the cause of thyroid dysfunction.²

The presence of antibodies directed against TPO is abnormal. While the precise cause is unknown, several hypotheses have been put forward to explain this flaw in immune system function.² In general, these hypotheses include an inciting cause followed by a process that mediates the autoimmune process. Possible inciting causes include viral illness, genetic predisposition, thyroid injury (e.g., infection, radiation, drug action), changes in circulating sex steroids, changes occurring during pregnancy, and excessive iodine intake.^2-6

Regardless of cause, antibodies directed against TPO cause lymphocytes to infiltrate the thyroid gland, destroying thyroid follicles. This may lead to fibrosis and areas of follicle hyperplasia. Moreover, TPO antibodies can destroy thyroid cells and may inhibit the activity of TPO directly.^7,8 These processes often lead to progressive hypothyroidism.²

Greater than 90 percent of people with Hashimoto’s thyroiditis (i.e., chronic autoimmune thyroiditis) have high concentrations of TPO antibodies in their blood.⁹ More than half of individuals with Graves’ disease have TPO antibodies. TPO antibodies may be detectable in people with subclinical hypothyroidism; their presence indicates an increased risk of developing overt hypothyroidism.¹⁰ Hypothyroidism occurs in approximately 1 to 2 percent of all pregnancies, and the most common cause of hypothyroidism in this patient population is Hashimoto’s thyroiditis.¹¹ TPO antibodies are able to cross the placenta, thus these antibodies may be present in fetuses born to mothers with circulating TPO antibodies.¹¹

TPO antibody levels may be measured in conjunction with other thyroid function tests (e.g., TSH, free T4) when an autoimmune mechanism is suspected. TPO antibodies are usually measured with other autoantibodies that would affect thyroid function, namely antibodies directed against thyroglobulin (Tg), thyroid-stimulating immunoglobulin (TSI), and the TSH receptor (TRAb).^12,13

PATHOLOGICAL/CONVENTIONAL RANGE INDICATIONS:

High in:^2,9-11,14-16

Hashimoto’s thyroiditis/chronic autoimmune hypothyroidism
- Goitrous autoimmune thyroiditis
- Atrophic autoimmune thyroiditis
Graves’ disease
Subclinical hypothyroidism
Pregnancy (abnormal)
Neonatal period (transient)
Postpartum thyroiditis
Painless (silent) thyroiditis

Low in:

Not applicable

FUNCTIONAL RANGE INDICATIONS:

High in:

No functional range

Low in:

Not applicable

References: