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Investigations in hyperthyroidism

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

Thyroid function tests consist of:

  • serum TSH -
    • has the highest sensitivity and specificity for hyperthyroidism
    • is the initial investigations in majority of patients with suspected thyrotoxicosis (if thyrotoxicosis is strongly suspected, serum TSH, free T4, and total T3 are assessed at the initial evaluation) (1,2)
    • levels of TSH are low and normal concentration nearly always excludes the diagnosis of thyrotoxicosis; the rare exceptions to this are a TSH-producing pituitary tumour or thyroid hormone resistance syndrome.
  • free thyroxine (T4) & free or total triiodothyronine (T3)

In addition the following investigations can be carried out:

  • serum levels of antibodies to the TSH receptor
    • useful to establish the diagnosis of Graves disease (especially when a radionuclide thyroid scan cannot be performed)
    • antibodies measured with immunoassay method (3rd generation) has a sensitivity of 98% and a specificity of 99% for diagnosis of Graves’ disease
  • thyroid peroxidase and thyroglobulin autoantibodies
    • thyroid peroxidase antibodies are present only in about 75% of cases of Graves’ disease
  • radioactive iodine uptake and scan
    • uptake is the percentage of an iodine 123 (I-123) tracer dose taken up by the thyroid gland, ranging from 15% to 25% at 24 hours.
    • uptake is very low (0% to 2%) in thyroiditis while it is high in Graves disease, a toxic adenoma, or a toxic multinodular goiter
  • thyroid ultrasound scan
    • useful as a cost effective and safe alternative for radioactive scan
    • useful during pregnancy, lactation, and in amiodarone-induced thyrotoxicosis (1,2,3)

Other investigations:

  • FBC:
    • normochromic normocytic anaemia may be seen in Graves' disease
  • ESR:
    • raised in Graves' disease
    • high in subacute thyroiditis
  • calcium - often raised
  • LFTs - may be abnormal in Graves' disease (4)

Reference:

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