THYROID PEROXIDASE

Code
900.5250
Name
THYROID PEROXIDASE
Category
None
Department
Send-Out
Start Date
Expiration Date
Synonyms
Thyroid Antibody; TPO Antibody; Anti-Microsomal Antibody
CPT Codes
86376
Site
SBMF
Reference Test
30019
ATLAS Test Code

Specimen Information

Type

Gold SST

Volume

1.0 ml

Transport Info

Refrigerated

Fasting Required?
False
Patient Instructions

Reference Range

0.0-35.0 IU/mL

Methodology

Quantitative Chemiluminescent Immunoassay (CLIA)

Clinical Significance

Primarily used to diagnose autoimmune thyroiditis.
Thyroid peroxidase is a 107,000 MW membrane-bound glycoprotein with a heme prosthetic group that catalyzes the iodide oxidation of tyrosine residues on thyroglobulin in the synthesis of the iodothyronines T3 and T4. Thyroid perioxidase is now generally recognized as the principal autoantibody protein in thyroid microsomes and until recently was known as thyroid antimicrosomal antigen. The nucleotide sequence for human thyroid peroxidase cDNA has been reported to code for a protein of 933 amino acids. The protein has hydrophobic domains at the amino and carboxy termini, which are consistent with it being a membrane associated protein. Titers of microsomal antibodies and TPO antibodies in sera have correlated very well in patients with autoimmune thyroid disease.A genetically engineered soluble form of TPO containing the extracellular region of TPO but lacking the transmembrane and intra-cytosplasmic regions has been developed and provides an easily reproducible source of purified protein for use in the diagnostic detection of TPO autoantibodies. This recombinant TPO has been demonstrated to recognize TPO autoantibodies in patients to the same extent as full-length membrane associated TPO. Autoimmune thyroid disease B cell epitopes on human TPO have been shown to be directed to the amino acid regions between 456 and 845 (up to the junction of the plasma membrane) on the 933 amino acid protein.The autoantibodies to human TPO are heterogeneous. The proportions of subclasses (IgG 1-4, IgM) are different from patient to patient as are their affinities. The majority of TPO autoantibodies, as with all antibodies, have been found to be directed against non-linear discontinuous conformational epitopes, although there are linear epitopes. Autoantibodies to TPO also have been demonstrated to inhibit enzymatic activity and cross-react with other peroxidases. Thyroid peroxidase autoantibodies are of pathological importance because they are present in the majority of Hashimoto’s thyroiditis patients and correlate with the active phase of the disease. Unlike thyroglobulin autoantibodies, they may damage thyroid cells by complement fixation.

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