Thyroid Peroxidase Antibody (now carried out in Biochemistry)

Alternative name: anti-TPO, formerly Anti-Throid Microsomal Antibody
Description: Most sera of patients with autoimmune thyroid disease contain autoantibodies recognising thyroglobulin and thyroid microsomal antigens, particularly the thyroid peroxidase a 110kDa, haem containing, peroxidase enzyme found on intracellular membranes of the epithelial cells of the follicles The autoantibodies are present in high levels.The most common autoimmune thyroid disorders are Graves’ disease (autoimmune hyperthyroiditis – increased thyroid secretion) which affects 3 in 1000 women, mostly aged between 30-50 and Hashimotos disease (autoimmune thyroiditis) causing thyroid atrophy which affects around 3 in 1000 women usually aged 40-60. The autoantibodies are usually IgG. Autoimmune thyroiditis may be associated with other autoimmune diseases especially pernicious anaemia or myasthenia gravis.
Indication: Autoimmune thyroid diseases.
Interpretation: Anti-thyroid microsomal antibodies are detected in high levels in:

  • 85-100% of patients with overt autoimmune thyroiditis (Hashimotos thyroiditis)
  • 70-90% of patients with Graves disease
  • 60% of patients with primary hypothyroidism
  • 30-60% of patents with pernicious anaemia but no overt thyroid disease

They are detected in low levels in 2-8% of normal individuals more frequently in the elderly and more often in women than men. Some of these indivduals will go on to develope autoimmune thyroiditis

Antithyroid antibodies are frequently found in patients with other autoimmune diseases e.g

  • Pernicious anaemia: 30-60%
  • Addisons disease: 28-40%
  • Type 1 Diabetes mellitus: 40%
  • Myasthenia gravis: 50%
  • Lambert-Eaton syndrome: 30%
Sample: Serum Separator Tube (SST)
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Analysing laboratory: Immunology The James Cook University Hospital