Approach to a low TSH level: Patience is a virtue

Abstract

Confronted with a low serum level of thyrotropin (thyroid-stimulating hormone, TSH), physicians should not jump to the conclusion that it is due to a hyperthyroid state, as other conditions and some drugs can be associated with a TSH level that is slightly low (0.1–0.4 μIU/mL) or frankly suppressed (<>

Key points

A low TSH value should always be followed up by measuring the thyroid hormones, ie, thyroxine (T₄) and triiodothyronine (T₃).

Serum levels of free thyroid hormones should be used when interpreting an abnormal TSH level, especially in the acute and inpatient settings.

A low TSH level is not always the result of suppression by elevations in circulating thyroid hormones.

A low TSH level in the setting of normal levels of free thyroid hormones should always be reassessed in 4 to 6 weeks before making a diagnosis.

Overt hyperthyroidism is usually associated with a frankly suppressed TSH (<>

• Copyright© 2010 The Cleveland Clinic Foundation