Investigations in hyperthyroidism

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:

• (1) Ross DS et al. 2016 American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis. Thyroid. 2016;26(10):1343-1421
• (2) Kravets I. Hyperthyroidism: Diagnosis and Treatment. Am Fam Physician. 2016;93(5):363-70.
• (3) Vaidya B, Pearce SH. Diagnosis and management of thyrotoxicosis. BMJ. 2014;349:g5128
• (4) Endocr Pract. 2000 Sep-Oct;6(5):367-9