Situations where the serum TSH is elevated but the patient is euthyroid:
(1) early recovery from serious illness (euthyroid sick syndrome)
(2) heterophile antibody to the animal species used in the testing system
(3) some patients with iodine deficiency
(4) adrenal insufficiency
(5) severe psychiatric illness
(6) macro-TSH
Situations where the serum TSH is elevated but the patient is hyperthyroid:
(1) pituitary resistance to thyroid hormone (partial or complete failure of the feedback loop)
(2) pituitary adenoma (production unregulated by feedback loop)
(3) paraneoplastic syndrome with TSH-secreting tumor (production unregulated by feedback loop)
It is important not to treat a patient for hypothyroidism simply because the serum TSH is elevated.
