What is the next step in managing a patient with hyperthyroidism (elevated Thyroid-Stimulating Hormone (TSH)) and normal thyroxine (T4) levels while on Synthroid (levothyroxine) therapy?

Increase Your Levothyroxine Dose

Your elevated TSH (above normal range) with normal T4 while on Synthroid indicates you are receiving inadequate thyroid hormone replacement and need a dose increase. 1

Why Your Current Dose Is Insufficient

Your situation represents subclinical hypothyroidism on treatment—meaning your TSH remains elevated despite levothyroxine therapy, signaling that your current dose is not adequately suppressing your pituitary's demand for more thyroid hormone. 1 The normal T4 level is misleading here; TSH is the primary marker for assessing thyroid hormone replacement adequacy, and yours indicates undertreatment. 1, 2

Immediate Action Required

Increase your levothyroxine dose by 12.5-25 mcg, with the specific increment depending on your current dose and clinical characteristics. 1

• For patients under 70 years without cardiac disease: Use 25 mcg increments for more efficient titration. 1
• For patients over 70 years or with cardiac disease: Use smaller 12.5 mcg increments to avoid cardiac complications. 1

Monitoring Timeline

• Recheck TSH and free T4 in 6-8 weeks after the dose adjustment, as this represents the time needed to reach a new steady state with levothyroxine's long half-life. 1, 3
• Target TSH range: 0.5-4.5 mIU/L with normal free T4 levels. 1
• Do not recheck labs earlier than 6 weeks, as adjusting doses before steady state leads to inappropriate management. 1

Common Causes to Rule Out First

Before increasing your dose, verify these potential causes of elevated TSH:

• Poor medication adherence: The most common cause of persistent TSH elevation in treated patients. 2 Take levothyroxine on an empty stomach, 30-60 minutes before breakfast, with a full glass of water. 1, 3
• Medication interference: Iron, calcium supplements, and antacids decrease levothyroxine absorption—take these at least 4 hours apart from your thyroid medication. 1, 3
• Recent illness or stress: Transient TSH elevations can occur during recovery from acute illness; if you were recently sick, consider rechecking in 3-6 weeks before adjusting. 1
• Enzyme-inducing medications: Certain drugs increase levothyroxine metabolism, requiring higher doses. 4

Why This Matters for Your Health

Persistent TSH elevation, even with normal T4, carries significant health risks:

• Cardiovascular dysfunction: Hypothyroidism causes delayed cardiac relaxation and abnormal cardiac output. 1
• Adverse lipid profiles: Elevated cholesterol levels that may improve with adequate treatment. 1
• Quality of life deterioration: Persistent fatigue, weight gain, cold intolerance, and cognitive symptoms. 1
• Progression risk: If your TSH is >10 mIU/L, you have approximately 5% annual risk of progressing to overt hypothyroidism. 1

Critical Pitfalls to Avoid

• Do not rely on T4 levels alone to assess thyroid replacement adequacy—TSH is the primary marker. 5 Some patients maintain normal T4 levels while remaining clinically hypothyroid due to inadequate dosing. 5
• Do not accept "watchful waiting" if your TSH is persistently elevated on repeat testing—this represents true undertreatment requiring dose adjustment. 1
• Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism, which increases risks for atrial fibrillation, osteoporosis, and cardiac complications. 1 Approximately 25% of patients on levothyroxine are unintentionally overtreated. 1

Long-Term Management

Once your TSH normalizes:

• Monitor TSH annually or sooner if symptoms change. 1
• Maintain consistent levothyroxine brand when possible, as bioequivalence can differ among generics. 4
• Notify your physician before any surgery or if starting new medications. 3