Which of the following is the most useful investigation for thyroid function?
Best thyroid function test is TSH as it helps in differentiating between primary and secondary thyrotoxicosis. The change of TSH values also indicates the improvement in the medical condition of the patient. For example, after resection of a pituitary adenoma secreting excess of TSH, the values of TSH will come back towards normal. Ref - Srb's manual of surgery 5e p483
TSH
T3
T4
Thyroglobulin
Endocrinology and breast