Anti-TPO antibodies (formerly - thyroid microsomal antibodies) are directed against a target protein - thyroid peroxidase (TPO) - located in the smooth endoplasmic reticulum of thyroid cells.

Thyroid peroxidase or Thyroperoxidase (TPO) is an enzyme mainly expressed in the thyroid that liberates iodine for addition onto tyrosine residues on thyroglobulin for the production of thyroxine (T4) or triiodothyronine (T3) (thyroid hormones). The presence of anti-TPO antibodies in serum is associated with thyroid autoimmune diseases (Graves' disease and Hashimoto's thyroiditis). Anti-TPO antibodies mostly belong to the IgG class.

Low to moderate levels of serum anti-TPO antibodies can be found in some other autoimmune pathology (eg systemic lupus erythematosus or Sjogren syndrom) and, rarely, in apparently healthy subjects (especially elderly women). Anti-TPO antibodies are more sensitive in diagnostics of thyroid autoimmune diseases than anti-thyroglobulin (anti-TG) antibodies. However, in some cases anti-TG positive sera may be negative for anti-TPO. Therefore, combined determination of both types of anti-thyroid antibodies (anti- TPO + anti-TG) provides a more sensitive laboratory diagnostic tool for thyroid autoimmunity.

Anti-TPO ELISA:

Immunoenzymatic colorimetric method (ELISA) for quantitative determination of Anti-TPO in serum or plasma.

Principle of the Assay:   

This test is based on two-site sandwich enzyme immunoassay principle. The microplates are coated with Streptavidin. In the first step the antigen Thyroid Peroxidase which is conjugated to Biotin binds to Streptavidin. Then the sample is placed into the microwells now coated by the antigen. Antibodies from the sample bind coated antigen on the microwell surface. Unbound material is removed by a washing procedure. Second antibodies directed against human IgG and labelled with horseradish peroxidase, are then added to the microwells. A second washing step is performed. Then the immune complex is visualized by adding Tetramethylbenzidine (TMB) substrate, which gives a blue reaction product. The intensity of this product is proportional to the amount of Anti-TPO in samples and standards. Sulphuric acid is added to stop the reaction. This produces a yellow endpoint colour. Absorption at 450 nm is read using an ELISA microwell plate reader.

Specific performance characteristics:  

Correlation with commercially available Anti-TPO assay performed on 36 samples is r = 0.96

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