From the Guidelines
Treatment with levothyroxine is typically initiated when the thyroid stimulating hormone (TSH) level exceeds 10 mIU/L, regardless of whether symptoms are present. This recommendation is based on expert opinion, as stated in the 2015 study published in the Annals of Internal Medicine 1, which suggests that a TSH level greater than 10.0 mIU/L is generally considered the threshold for initiation of treatment.
For patients with TSH levels between 4.5-10 mIU/L (subclinical hypothyroidism), treatment decisions should be individualized based on symptoms, presence of thyroid antibodies, and cardiovascular risk factors, as suggested by the 2004 study published in JAMA 1. In pregnant women or those planning pregnancy, treatment is recommended at lower thresholds (TSH >2.5 mIU/L) due to the importance of thyroid hormones in fetal development.
Some key considerations for levothyroxine treatment include:
- The standard starting dose for most adults is 1.6 mcg/kg/day (typically 50-100 mcg daily)
- Lower initial doses (12.5-25 mcg daily) for elderly patients or those with cardiac disease
- Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast
- Separation from medications that can interfere with absorption like calcium, iron supplements, and proton pump inhibitors
- Treatment efficacy is monitored by measuring TSH levels 6-8 weeks after starting therapy, with dose adjustments made to achieve a target TSH within the normal reference range (typically 0.4-4.5 mIU/L) 1.
It is essential to weigh the potential benefits and risks of treatment, particularly in patients with subclinical hypothyroidism, as the likelihood of improvement may be small and must be balanced against the inconvenience, expense, and potential risks of therapy 1.
From the Research
Treatment of Hypothyroidism with Levothyroxine
- The decision to start treatment with levothyroxine depends on the level of Thyroid-Stimulating Hormone (TSH) and the presence of symptoms suggestive of hypothyroidism 2.
- According to some practice guidelines, treatment with levothyroxine is recommended when the TSH level is above 10 mIU/L 2, 3.
- For patients with subclinical hypothyroidism, treatment is generally not necessary unless the TSH exceeds 7.0-10 mIU/L 4.
- The TSH goals are age-dependent, with a 97.5 percentile (upper limit of normal) of 3.6 mIU/L for patients under age 40, and 7.5 mIU/L for patients over age 80 4.
- Some studies suggest that treatment with levothyroxine may be beneficial for patients with subclinical hypothyroidism who have symptoms suggestive of hypothyroidism, anti-thyroid antibodies, increased lipids, and other risk factors 3.
Initiating Treatment with Levothyroxine
- Levothyroxine is usually started at a dose of about 1.5 microg/kg per day, taken on an empty stomach, for young adults 2.
- Elderly patients and those with coronary artery disease should start at a lower dose: 12.5 to 50 microg per day 2.
- Treatment monitoring is based mainly on blood TSH assay, and dose adjustment should only be considered after 6 to 12 weeks, given the long half-life of levothyroxine 2.