What is the target TSH level?

In general, thyroid hormone suppression therapy is targeted towards distinct levels of TSH suppression. Therapy at the greatest extreme aims to suppress TSH to an undetectable level, usually expressed as being less than 0.01 mU/L. Therapy at more moderate levels aims to suppress TSH either to just below the normal range (expressed as 0.1 - 0.5 mU/L) or the lower end of the normal range (expressed as 0.5 - 1.0 mU/L).

A number of factors are considered in determining the target range of suppression. If recurrent growth of thyroid cancer seems likely, TSH should be suppressed to an undetectable level. If the risk of recurrence seems low, it may be acceptable to suppress TSH to the lower end of the normal range.

The degree of attainable suppression may be limited by certain factors. If a patient receiving thyroid hormone suppression therapy develops palpitations, anxiety, shakiness, insomnia, or difficulty tolerating excessive heat during treatment, the dose of levothyroxine may need to be lowered. Certain preexisting conditions may also be exacerbated by high doses of levothyroxine. These include an irregular heartbeat, osteoporosis with thinning of the bones, or coronary artery disease leading to angina or a heart attack. When necessary to limit high dosage symptoms or to accommodate a history of preexisting conditions, lower doses of levothyroxine may be administered that do not produce as much suppression.

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