What is the appropriate next step in managing a 60-year-old man with primary hypothyroidism taking levothyroxine (Synthroid) 88 µg daily who now has a thyroid-stimulating hormone (TSH) of 4.64 mIU/L?

Increase Levothyroxine Dose to Normalize TSH

For a 60-year-old man with primary hypothyroidism on levothyroxine 88 µg daily with a TSH of 4.64 mIU/L, increase the levothyroxine dose by 12.5–25 µg to achieve a target TSH of 0.5–4.5 mIU/L. 1

Rationale for Dose Adjustment

Your patient's TSH of 4.64 mIU/L indicates inadequate thyroid hormone replacement while on levothyroxine 88 µg daily. 1 Although this TSH falls in the "subclinical hypothyroidism" range (TSH 4.5–10 mIU/L with normal free T4), patients already on levothyroxine therapy with elevated TSH require dose adjustment to normalize thyroid function into the reference range of 0.5–4.5 mIU/L. 1

The evidence supporting dose adjustment at this TSH level is particularly strong for patients already on treatment:

• Even TSH levels between 4.5–10 mIU/L warrant dose adjustment in patients on existing therapy, as the goal is to maintain TSH within the normal reference range. 1
• Persistent TSH elevation indicates the current dose is insufficient to meet the patient's thyroid hormone requirements. 1
• Untreated or undertreated hypothyroidism carries risks including persistent symptoms, adverse cardiovascular effects, and abnormal lipid metabolism. 1

Specific Dose Adjustment Protocol

Increase levothyroxine by 12.5–25 µg based on the patient's age and clinical characteristics:

• For this 60-year-old patient without cardiac disease, a 25 µg increment is appropriate (increasing from 88 µg to 112 µg or 113 µg daily). 1
• If the patient has cardiac disease or is over 70 years, use the smaller 12.5 µg increment to avoid cardiac complications. 1
• Larger dose adjustments should be avoided as they may lead to overtreatment, especially in elderly patients or those with cardiac disease. 1

Monitoring After Dose Adjustment

Recheck TSH and free T4 in 6–8 weeks after the dose increase, as this represents the time needed to reach steady state. 1 The target is:

• TSH within the reference range of 0.5–4.5 mIU/L 1
• Normal free T4 levels 1

Once the appropriate maintenance dose is established, monitor TSH annually or sooner if symptoms change. 1

Important Considerations Before Dose Adjustment

Rule out factors that may transiently elevate TSH:

• Recent acute illness or hospitalization 1
• Recovery phase from thyroiditis 1
• Recent iodine exposure (e.g., CT contrast) 1
• Medication changes affecting thyroid function 1

If any of these factors are present, consider repeating TSH in 3–6 weeks before adjusting the dose, as 30–60% of elevated TSH levels normalize spontaneously. 1

Critical Pitfalls to Avoid

• Do not ignore elevated TSH in a patient already on levothyroxine—this indicates inadequate replacement requiring dose adjustment. 1
• Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism, which increases risk for osteoporosis, fractures, atrial fibrillation, and cardiac complications. 1
• Do not adjust doses too frequently—wait the full 6–8 weeks between adjustments to allow steady state to be reached. 1
• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses that fully suppress TSH, increasing serious complication risks, so careful monitoring after dose adjustment is essential. 1