What is the recommended increase in levothyroxine (T4) dose for a patient with a Thyroid Stimulating Hormone (TSH) level of 5.88 who was previously stable on 75mcg of levothyroxine (T4)?

Levothyroxine Dose Adjustment for TSH 5.88

Increase levothyroxine by 12.5-25 mcg (from 75 mcg to either 87.5 mcg or 100 mcg) to normalize TSH into the reference range of 0.5-4.5 mIU/L. 1

Rationale for Dose Adjustment

Your TSH of 5.88 mIU/L indicates inadequate thyroid hormone replacement despite previous stability on 75 mcg. 1 This level represents subclinical hypothyroidism in a patient already on treatment, signaling the current dose is insufficient. 1

• For patients with TSH 4.5-10 mIU/L already on levothyroxine therapy, dose adjustment is reasonable to normalize TSH into the reference range (0.5-4.5 mIU/L). 1
• The recommended increment for dose adjustment is 12.5-25 mcg based on your current dose of 75 mcg. 1
• Larger adjustments should be avoided as they may lead to overtreatment and iatrogenic hyperthyroidism. 1

Specific Dosing Strategy

For patients under 70 years without cardiac disease:

• Use the larger increment of 25 mcg (increasing from 75 mcg to 100 mcg). 1
• More aggressive titration is appropriate in this population. 1

For patients over 70 years or with cardiac disease:

• Use the smaller increment of 12.5 mcg (increasing from 75 mcg to 87.5 mcg). 1
• Smaller increments avoid potential cardiac complications including angina, arrhythmias, and cardiac decompensation. 1, 2

Monitoring Protocol

• Recheck TSH and free T4 in 6-8 weeks after dose adjustment. 1, 2
• This 6-8 week interval is critical because it represents the time needed to reach a new steady state after any levothyroxine dose change. 1
• Target TSH should be within the reference range (0.5-4.5 mIU/L) with normal free T4 levels. 1
• Once the appropriate maintenance dose is established, monitor TSH annually or sooner if symptoms change. 1

Why Your TSH Rose Despite Previous Stability

Several factors can cause TSH elevation in previously stable patients:

• Confirm the elevation with repeat testing, as 30-60% of elevated TSH levels normalize spontaneously on repeat measurement. 1
• Review for recent iodine exposure (such as CT contrast), which can transiently affect thyroid function. 1
• Assess medication adherence and timing of levothyroxine administration. 1
• Consider drug interactions or malabsorption issues that may have developed. 1, 2
• Weight gain increases levothyroxine requirements. 1

Critical Pitfalls to Avoid

• Do not adjust doses too frequently before reaching steady state—always wait 6-8 weeks between adjustments. 1
• Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism, which increases risk for osteoporosis, fractures, atrial fibrillation, and cardiac complications. 1
• Never treat based on a single elevated TSH value without confirmation, as transient elevations are common. 1
• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, highlighting the importance of careful dose titration. 1

Special Considerations

If you have cardiac disease or atrial fibrillation:

• More frequent monitoring may be warranted—consider repeating testing within 2 weeks rather than waiting 6-8 weeks. 1
• Use the smaller 12.5 mcg increment to minimize cardiac risk. 1

If you are planning pregnancy:

• More aggressive normalization of TSH is warranted, as subclinical hypothyroidism during pregnancy is associated with adverse outcomes including preeclampsia and low birth weight. 1
• Levothyroxine requirements typically increase 25-50% during pregnancy. 1, 2