The lower limit of detection of serum TSH in most currently used sensitive RlAs is 0.05ΓÇô0.1mu/l, while some assays can detect levels as low as 0.005mu/l. The range of basal TSH in the normal healthy population is 0.4ΓÇô5mu/l, with a median of approximately 2mu/l. Basal TSH in always suppressed in hyperthyroidism, unless the hyperthyroidism is driven by the pituitary (pituitary adenomas or pituitary T3 resistance) or an artifact is present in the assay. Suppression of TSH, usually to undetectable levels or 0.1mu/l, is currently considered the sine qua non for diagnosis of hyperthyroidism.
