Initial management of primary hypothyroidism in adults

This algorithm depicts an approach to the initial treatment of primary hypothyroidism, defined as a high TSH and a low free T4. The algorithm is not intended for use in patients with transient hypothyroidism (eg, postpartum thyroiditis) or central hypothyroidism. In central hypothyroidism, serum TSH levels are typically low or inappropriately normal, but TSH may be slightly elevated due, in part, to the secretion of TSH that has reduced biologic activity but normal immunoactivity. Refer to other UpToDate content on thyroiditis and central hypothyroidism.

TSH: thyroid-stimulating hormone; ULN: upper limit of normal; T4: thyroxine.

* Assumes adherence to medication regimen.

¶ There is an age-related shift toward higher TSH concentrations in older patients (≥70 years), with a ULN of approximately 7.5 mU/L in 80 year olds. Older patients with a TSH up to 7.5 mU/L may not require a dose increase, and treatment resulting in TSH levels under 1 mU/L should be avoided.

Δ Switching between levothyroxine manufacturers does not usually necessitate remeasuring TSH. We typically reserve remeasuring TSH for those concerned about efficacy or if it is important to maintain the serum TSH within a narrow range (eg, thyroid cancer treatment).

◊ Symptoms of hypothyroidism may include cold intolerance, fatigue, constipation. Symptoms of hyperthyroidism may include palpitations, heat intolerance, tremulousness. Refer to UpToDate topics on clinical manifestations of hypothyroidism and hyperthyroidism.

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Initial management of primary hypothyroidism in adults