Thyroid peroxidase antibodies

Thyroid peroxidase antibodies ( TPO-AK , also microsomal antibodies , MAK ) are antibodies directed against thyroid peroxidase , the serum level of which can be increased in various autoimmune thyroid disorders .

Thyroid peroxidase plays an important role in the synthesis of thyroid hormones . The enzyme is located in the apical cell membrane of the thyroid cell, that is, on the side of the cell that faces the thyroid follicle. The antibodies detectable in autoimmune thyroid disease are directed against the extracellular part of thyroid peroxidase. It is not clear how the thyroid peroxidase leaves the apical cell side or the contents of the thyroid follicle and thus becomes accessible to the immune system .

proof

Thyroid peroxidase antibodies can be detected using various quantitative immunassay methods , including radioimmunoassays (RIA and IRMA) and ELISA methods . Recombinant thyroid peroxidase serves as the antigen in these tests . The measurement result is given in international units per liter (IU / l). Despite the usual referencing with a standard of the Medical Research Council , the measurement results of different laboratories are only partially comparable.

Occurrence

Thyroid peroxidase antibodies are detectable in over 90 percent of patients with chronic autoimmune thyroiditis ( Hashimoto's thyroiditis ) and over 70% of patients with active Graves' disease . However, the antibody titers are only marginally or slightly increased in about 30 percent of the sick . As slightly increased values can also occur in around 20 percent of patients with non-autoimmune thyroid diseases ( e.g. goiter nodosa or thyroid autonomy ) as well as in healthy euthyroid people, the specificity is limited: if thyroid peroxidase antibodies with a low titer are detected, it cannot Inevitably, the presence of an autoimmune thyroid disease must be concluded.

Multiple autoimmune diseases in the same patient occasionally occur. Three percent of all patients with type 1 diabetes have overt hypothyroidism, and 13 to 34 percent have positive thyroid peroxidase antibodies and, at the same time, elevated TSH .

Clinical value

If Hashimoto's thyroiditis is functionally and sonographically clear (marked hypothyroidism, small and hypoechoic thyroid gland), the additional determination of the thyroid peroxidase antibodies can usually be dispensed with. In less clear situations, however, elevated thyroid peroxidase antibodies can contribute to the diagnosis. In patients suspected of having Graves' disease but who are negative for TSH receptor antibodies , elevated thyroid peroxidase antibodies can also be an important diagnostic clue to the cause of the hyperthyroidism.

Patients with elevated thyroid peroxidase antibody titers but currently normal thyroid metabolism ( euthyroidism ) are recommended to have their TSH level determined annually, as they have a five percent chance of developing hypofunction per year. Because of the special importance of maternal thyroid hormones for the child, pregnant women with positive thyroid peroxidase antibodies should even have their TSH determined once in the trimester . Patients with autoantibodies of the thyroid gland are also at increased risk of developing postpartum thyroiditis .

Women with thyroid peroxidase antibodies are at increased risk of miscarriage or premature birth. A meta-analysis from 31 studies showed an increase in the risk of miscarriage by a factor of 3.9 and an increase in the risk of premature birth by a factor of 2.07 in pregnant women with thyroid peroxidase antibodies. The hope that the administration of levothyroxine in pregnant women with antibodies to increase the rate of full term pregnancies has not been confirmed in a recent study.

swell

Lothar-Andreas Hotze, Petra-Maria Schumm-Draeger. Thyroid diseases. Diagnosis and therapy. Berlin 2003 ISBN 3-88040-002-4

Individual evidence

↑ Mariotti et al .: antithyroid peroxidase autoantibodies in thyroid diseases. J Clin Endocrinol Metab . 1990; 71 (3): 661-9. PMID 2168432
↑ Shakila Thangaratinam, Alex Tan, Ellen Knox, Mark D Kilby, Jayne Franklyn: Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence . In: BMJ (Clinical research ed.) . tape 342 , May 9, 2011, ISSN 1756-1833 , p. d2616 , doi : 10.1136 / bmj.d2616 , PMID 21558126 , PMC 3089879 (free full text).
^ Rima K. Dhillon-Smith, Lee J. Middleton, Kirandeep K. Sunner, Versha Cheed, Krys Baker: Levothyroxine in Women with Thyroid Peroxidase Antibodies before Conception . In: New England Journal of Medicine . tape 380 , no. 14 , April 4, 2019, ISSN 0028-4793 , p. 1316–1325 , doi : 10.1056 / NEJMoa1812537 ( nejm.org [accessed April 8, 2019]).

[1] Mariotti et al .: antithyroid peroxidase autoantibodies in thyroid diseases. J Clin Endocrinol Metab . 1990; 71 (3): 661-9. PMID 2168432

[2] Shakila Thangaratinam, Alex Tan, Ellen Knox, Mark D Kilby, Jayne Franklyn: Association between thyroid autoantibodies and miscarriage and preterm birth: meta-analysis of evidence . In: BMJ (Clinical research ed.) . tape 342 , May 9, 2011, ISSN 1756-1833 , p. d2616 , doi : 10.1136 / bmj.d2616 , PMID 21558126 , PMC 3089879 (free full text).

[3] Rima K. Dhillon-Smith, Lee J. Middleton, Kirandeep K. Sunner, Versha Cheed, Krys Baker: Levothyroxine in Women with Thyroid Peroxidase Antibodies before Conception . In: New England Journal of Medicine . tape 380 , no. 14 , April 4, 2019, ISSN 0028-4793 , p. 1316–1325 , doi : 10.1056 / NEJMoa1812537 ( nejm.org [accessed April 8, 2019]).