Thyroid disorders affect approximately 20 million Americans — predominantly women — with hypothyroidism alone affecting 5% of the population. Despite being among the most commonly managed endocrine conditions, significant practice variation exists around TSH targets, combination T3/T4 therapy, and the treatment of subclinical thyroid disease. The 2023 ATA clinical practice guidelines updated several key recommendations.
Hypothyroidism: TSH Targets and T4 vs. T3/T4
Levothyroxine (LT4) remains the standard treatment — with TSH target of 0.5–2.5 mIU/L in most adults, with higher acceptable range (up to 4.0 mIU/L) in patients ≥70 years and those with coronary artery disease (risk of arrhythmia with overtreatment). The T3/T4 combination therapy question: approximately 5–10% of patients on LT4 with normal TSH report persistent hypothyroid symptoms. These patients often have lower free T3 levels despite normal TSH due to impaired T4→T3 conversion. Two large RCTs of LT4+LT3 combination showed quality of life improvement in a subset — the ATA 2023 guidelines now grade combination therapy as "weak recommendation" for a trial in symptomatic patients despite adequate LT4. Deiodinase 2 (DIO2) polymorphism (Thr92Ala): identifies patients likely to benefit from combination therapy, though routine testing isn't yet standard of care. Armour Thyroid (desiccated thyroid extract): contains both T4 and T3 — some patients prefer it, evidence shows comparable thyroid hormone levels to LT4 in equivalently dosed comparisons.
Subclinical Thyroid Disease and Hyperthyroidism
Subclinical hypothyroidism (high TSH, normal FT4): treatment benefit is well-established for TSH >10 mIU/L. For TSH 5–10: benefit in young patients with symptoms or thyroid antibodies; no clear benefit in asymptomatic older adults (TRUST trial showed no quality of life improvement in ≥65 year-olds). Graves' disease: antithyroid drugs (methimazole, PTU) vs. radioactive iodine (RAI) vs. surgery — all are acceptable. 2023 ATA guidance increasingly favors longer methimazole trials (18–24 months) to achieve durable remission before RAI or surgery. Teprotumumab (Tepezza) for active thyroid eye disease: RCTs show 71% reduction in proptosis — a significant advance. For clinical facilities managing endocrine patients, our diagnostic equipment section and laboratory supplies section support thyroid function testing workflows.
