thyroid disease diagnostic algorithm

Last edited 04/2021 and last reviewed 04/2022

Where TSH and free T3 or T4 are measured as the first-line thyroid investigation there are six patterns of abnormality:

  • TSH may be high or low
  • free T3 or free T4 may be low, normal or high


  • Dayan CM. Interpretation of thyroid function tests. Lancet 2001;357:619-24.