The Normal TSH Reference Range: What Has Changed in the Last Decade?

Serum TSH assessment is the most sensitive screeningtest for the diagnosis of thyroid dysfunction in theabsence of pituitary or hypothalamic disease. This test hasbeen used increasingly in the last decade to detect subclinicalthyroid dysfunction (STD). Recent data suggest that STD isa common disorder that may be associated with importantadverse events (1–5). The American Association of ClinicalEndocrinologists (AACE) and American Thyroid Association(ATA) 2012 guidelines recommend treatment of subjectswith persistent increased serum TSH levels10 mIU/Land undetectable serumTSH(0.1 mIU/L) (6, 7). The treatmentof mild thyroid hormone excess (TSH 0.1–0.4 mIU/L)or deficiency (serumTSH10mIU/L) is controversial (1, 2).However, what is the normal TSH reference range? Obviously,this issue is critical in deciding whether or not to treatpatients with mild STD and in identifying individuals withhigh-normal or low-normal serum TSH. It is also importantin defining the TSH target level in patients receiving thyroidhormone replacement therapy