Thyroid‐specific peroxidase (TPO) is present on the microsomes of thyrocytes and
is expressed at its apical cell surface. In synergy with thyroglobulin (Tg) this
enzyme has an essential function in the iodination of L‐tyrosine and the chemical
coupling of the resulting mono‐ and di‐iodotyrosine to form the thyroid hormones
T4, T3, and rT3.
TPO is a potential autoantigen. Elevated serum titers of antibodies to TPO are
found in several forms of thyroiditis caused by autoimmunity. The still frequently
found term “microsomal antibody” originates from the time when TPO had not yet
been identified as an antigen in autoimmunity caused by microsomes. In the
clinical sense the two terms anti‐TPO and microsomal antibody can be used
synonymously; there are differences, however, with regard to the test methods.
High anti‐TPO titers are found in up to 90 % of patients with chronic Hashimoto's
thyroiditis. In Graves' disease, 70 % of the patients have an elevated titer.
Although the sensitivity of the procedure can be increased by simultaneously
determining other thyroid antibodies (anti‐Tg, TSH‐receptor‐antibody - TRAb), a
negative finding does not rule out the possibility of an autoimmune disease. The
magnitude of the antibody titer does not correlate with the clinical activity of the
disease. Initially elevated titers can become negative after lengthy periods of
illness or during remission. If antibodies reappear following remission, then a
relapse is probable.
Whereas the usual microsomal antibody tests employ unpurified microsomes as
an antigen preparation, the anti‐TPO tests use a purified peroxidase. The two
procedures are of comparable performance in terms of clinical sensitivity, but
better lot‐to‐lot consistency and higher clinical specificity can be expected from
anti‐TPO tests due to the higher quality of the antigen used.
The Enzyme linked immunosorbent
Your message must be between 20-3,000 characters!
