From the FDA Drug Label
In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage. In patients with hypothyroidism, assess the adequacy of replacement therapy by measuring both serum TSH and total or free-T4. Monitor TSH and total or free-T4 in pediatric patients as follows: 2 and 4 weeks after the initiation of treatment, 2 weeks after any change in dosage, and then every 3 to 12 months thereafter following dosage stabilization until growth is completed
The monitoring frequency for thyroid function tests (TFTs) after changing the dose of levothyroxine is as follows:
- Adults: every 6 to 8 weeks after any change in dosage
- Pediatric patients: 2 weeks after any change in dosage, and then every 3 to 12 months thereafter following dosage stabilization until growth is completed 1
From the Research
Thyroid function tests (TFTs) should typically be checked 6-8 weeks after changing the dose of levothyroxine. This timeframe allows the body to reach a new steady state with the adjusted medication dose, as levothyroxine has a long half-life of approximately 7 days. After confirming that thyroid levels have stabilized at the target range, monitoring can be reduced to every 6-12 months for stable patients. However, more frequent monitoring may be necessary for certain populations:
- pregnant women may need checks every 4-6 weeks due to changing physiological demands;
- elderly patients or those with cardiac conditions might require more cautious follow-up;
- and patients with poor medication adherence or those taking medications that interact with levothyroxine absorption (such as calcium supplements, iron, or proton pump inhibitors) may need more frequent testing. The goal of monitoring is to maintain TSH within the reference range (typically 0.4-4.0 mIU/L for most adults), with slightly different targets for special populations like pregnant women or the elderly, as suggested by recent guidelines 2. If symptoms of hypothyroidism or hyperthyroidism persist despite normal lab values, reassessment may be warranted regardless of the typical monitoring schedule, considering the latest evidence on levothyroxine therapy 3, 4.