Levothyroxine Dose Increase Recommended
Yes, the patient should increase their levothyroxine dose from 112 mcg, as a TSH of 15 mIU/L with FT4 of 1.4 indicates inadequate thyroid hormone replacement requiring immediate dose adjustment. 1, 2
Rationale for Dose Increase
A TSH >10 mIU/L warrants dose adjustment regardless of symptoms, as this level of elevation carries approximately 5% annual risk of progression to overt hypothyroidism and is associated with increased cardiovascular risk. 1
The current TSH of 15 mIU/L clearly indicates undertreatment, even though the FT4 appears within normal range—TSH is the primary marker for monitoring levothyroxine therapy adequacy. 1, 2
Persistent TSH elevation >10 mIU/L despite levothyroxine therapy suggests the current dose is insufficient to meet the patient's thyroid hormone requirements. 1, 2
Recommended Dose Adjustment
Increase levothyroxine by 25 mcg daily (from 112 mcg to 137 mcg or the nearest available formulation strength). 1, 2
For patients under 70 years without cardiac disease, use 25 mcg increments for dose adjustments. 1
For patients over 70 years or with cardiac disease, use smaller 12.5 mcg increments to avoid cardiac complications. 1, 2
The target TSH should be within the reference range of 0.5-4.5 mIU/L. 1, 2
Monitoring Protocol
Recheck TSH and free T4 in 6-8 weeks after the dose adjustment to evaluate response. 1, 2
Free T4 helps interpret ongoing abnormal TSH levels during therapy, as TSH may take longer to normalize. 1
Once adequately treated with stable TSH, repeat testing every 6-12 months or if symptoms change. 1
Critical Considerations Before Dose Increase
Rule out adrenal insufficiency before increasing levothyroxine, particularly if the patient has any history of pituitary disease, autoimmune conditions, or is on immunotherapy—starting or increasing thyroid hormone before corticosteroids can precipitate adrenal crisis. 3, 1
If central hypothyroidism is suspected (low or normal TSH with low FT4), always start corticosteroids several days before thyroid hormone. 3
Check morning cortisol and ACTH if there is any suspicion of concurrent adrenal insufficiency. 3
Investigate Potential Causes of Elevated TSH
Before simply increasing the dose, consider factors that may be interfering with levothyroxine absorption:
Medication interactions: Calcium supplements, iron, proton pump inhibitors, bile acid sequestrants, and certain other medications can impair levothyroxine absorption. 4, 5
Timing of administration: Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast, without other medications. 4
Gastrointestinal disorders: Celiac disease, Helicobacter pylori infection, atrophic gastritis, inflammatory bowel disease, or previous bariatric surgery can reduce absorption. 4
Compliance issues: Non-adherence is a common cause of persistent hypothyroidism—consider whether the patient is actually taking the medication as prescribed. 6, 7
Common Pitfalls to Avoid
Do not delay treatment waiting for symptoms to develop—TSH >10 mIU/L requires dose adjustment regardless of symptom status. 1
Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism, which increases risk for atrial fibrillation, osteoporosis, and cardiac complications. 1
Do not adjust doses more frequently than every 6-8 weeks, as levothyroxine requires this time to reach steady state. 1
Never assume the patient is taking the medication correctly—approximately 25% of patients with elevated TSH have compliance or administration timing issues rather than true dose inadequacy. 6, 7
If TSH Remains Elevated After Dose Adjustment
If TSH remains >10 mIU/L after confirmed adherence and appropriate dose increase:
Consider a levothyroxine absorption test (1000 mcg oral dose with FT4 measured at baseline and 2 hours) to distinguish malabsorption from non-adherence. 6, 7
Evaluate for anti-gastric parietal cell antibodies, anti-endomysial antibodies, and tissue transglutaminase antibodies to screen for autoimmune gastritis and celiac disease. 4
Test for Helicobacter pylori infection, which can impair levothyroxine absorption. 4
Refer to gastroenterology if malabsorption is confirmed. 4