Raised TSH, normal free thyroid hormones

The large majority of patient with raised TSH and normal free thyroid hormones are suffering from subclinical autoimmune hypothyroidism.

These results occur more rarely in the following circumstances:

• the presence of heterophile antibodies
  • mouse antibodies are used in many TSH assays
  • patients may have antibodies to mouse immunoglobulins
  • heterophile antibodies result in a false TSH elevation
  • alternative assays should be used for these patients
    
    
• in patients taking a regular dose of thyroxine an increase in the TSH concentration may indicate thyroxine malabsorption, due to:
  • small bowel disease
  • cholestyramine
  • iron therapy
    
    
• amiodarone therapy
  
  
• recovery from severe non-thyroidal disease
  
  
• congenital abnormalities of thyroid function:
  • some cases of Pendred's syndrome

Reference

1. Thyroid Function Tests. British Thyroid Foundation, revised 2021