This site is intended for healthcare professionals
General Practice Notebook
Medical search

investigations in hypothyroidism

FREE subscriptions for doctors and students... click here
You have 3 open access pages.

  • primary hypothyroidism is indicated by an increase in serum TSH concentration above the upper limit of the reference range combined with free T4 levels below the reference range (1,2)
    • in overt hypothyroidism - serum TSH above 10 mU/L + free T4 below the reference range
    • in subclinical hypothyroidism - serum TSH above the reference range + free T4 within the reference range, the test should be repeated after 3-6 months to exclude transient causes of raised TSH (2)
  • free or total serum T3 is generally unhelpful since it may be only slightly reduced in severe hypothyroidism, or may be elevated by illness unrelated to thyroid function, or as a consequence of incorrect drug therapy
  • secondary hypothyroidism is suggested by reduced free or total T4 and TSH below or within normal range; other tests for hypothalamic / pituitary function are necessary
  • other tests of thyroid function - e.g. thyroidal uptake tests, serum cholesterol have limited value in the diagnosis
  • primary myxoedema may demonstrate a normal or exaggerated response of TSH to TRH; a negative TSH response excludes primary hypothyroidism but not a secondary cause
  • antithyroid antibodies are suggestive of aetiology only, screening for antithyroid antibody is also useful in
    • predicting subsequent hypothyroidism in subclinical hypothyroid patients, in pregnant women and post partum women
    • for differential diagnosis of diffuse goitre (3)

Other possible abnormal laboratory tests include:

  • normochromic macrocytic anaemia
  • low sodium
  • increased prolactin
  • CK, AST and LDH may be elevated (due to abnormal muscle membranes) (3)

Reference:

Links:

General Practice Notebook
General Practice Notebook
The information provided herein should not be used for diagnosis or treatment of any medical condition. A licensed medical practitioner should be consulted for diagnosis and treatment of any and all medical conditions. Copyright 2016 Oxbridge Solutions LtdĀ®. Any distribution or duplication of the information contained herein is strictly prohibited. Oxbridge Solutions LtdĀ® receives funding from advertising but maintains editorial independence. GPnotebook stores small data files on your computer called cookies so that we can recognise you and provide you with the best service. If you do not want to receive cookies please do not use GPnotebook.