What is the next step for a patient with elevated TSH levels on Synthroid (levothyroxine) 88mcg/day?

Increase Levothyroxine Dose by 12.5-25 mcg

Your TSH of 6.10 mIU/L on Synthroid 88 mcg/day indicates inadequate thyroid hormone replacement, requiring a dose increase to normalize TSH into the target range of 0.5-4.5 mIU/L. 1

Recommended Dose Adjustment

Increase your levothyroxine dose by 12.5-25 mcg based on your age and cardiac status:

• If you are under 70 years old without heart disease: Increase by 25 mcg (to 112 mcg or 113 mcg daily) for more efficient TSH normalization 2, 1
• If you are over 70 years old or have cardiac disease/multiple comorbidities: Increase by only 12.5 mcg (to 100 mcg daily) to avoid cardiac complications 2, 1

The most common increment would be moving from 88 mcg to either 100 mcg or 112 mcg, depending on your clinical characteristics 2

Why This Dose Increase Is Necessary

• TSH persistently above 6 mIU/L in a patient already on levothyroxine indicates the current dose is insufficient and warrants adjustment 1
• This TSH level carries approximately 5% annual risk of progression to overt hypothyroidism 2, 1
• Even subclinical hypothyroidism (elevated TSH with normal free T4) in patients already on thyroid replacement therapy should be treated to normalize TSH 1
• Persistent undertreatment risks include ongoing hypothyroid symptoms, adverse effects on cardiovascular function, lipid metabolism, and quality of life 2

Monitoring After Dose Adjustment

Recheck TSH and free T4 in 6-8 weeks after the dose increase to allow sufficient time to reach steady-state levels 2, 1:

• This 6-8 week interval is critical because levothyroxine has a long half-life of 6-7 days, requiring this duration to reach a new steady state 3
• Target TSH should be within the reference range of 0.5-4.5 mIU/L with normal free T4 levels 2, 1
• Free T4 measurement helps interpret ongoing abnormal TSH levels during therapy, as TSH may take longer to normalize 2

Once adequately treated, repeat testing every 6-12 months or if symptoms change 2

Critical Pitfalls to Avoid

• Do not adjust doses too frequently before reaching steady state (wait the full 6-8 weeks between adjustments) to avoid inappropriate dosing 2, 1
• Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism, increasing risk for atrial fibrillation, osteoporosis, fractures, and cardiac complications 2, 1
• Do not ignore symptoms: Even with subclinical hypothyroidism, fatigue or other hypothyroid complaints warrant treatment consideration 1
• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, highlighting the importance of appropriate dose titration 2

Medication Adherence Considerations

Before increasing the dose, confirm you are taking levothyroxine correctly 4, 5:

• Take as a single dose on an empty stomach, one-half to one hour before breakfast with a full glass of water 3
• Do not take within 4 hours of iron, calcium supplements, or antacids, as these decrease levothyroxine absorption 3
• Poor adherence is the most common cause of persistent TSH elevation in patients on thyroid hormone replacement 5

Special Population Considerations

If you are pregnant or planning pregnancy: More aggressive TSH normalization is warranted, as subclinical hypothyroidism during pregnancy is associated with adverse outcomes including preeclampsia, low birth weight, and potential neurodevelopmental effects 2, 1

If you have cardiac disease or are elderly: Use smaller dose increments (12.5 mcg) and monitor more carefully for cardiac symptoms such as chest pain, palpitations, or shortness of breath 2, 1