Increase the Desiccated Thyroid Dose
Your patient's TSH of 4.91 mIU/L indicates inadequate thyroid hormone replacement, and the dose should be increased. Even though T3 and T4 are normal, the elevated TSH demonstrates that her pituitary is signaling for more thyroid hormone, meaning she remains biochemically hypothyroid 1.
Why This TSH Level Requires Action
- TSH 4.91 mIU/L exceeds the upper limit of normal (0.45-4.5 mIU/L), indicating subclinical hypothyroidism despite being on replacement therapy 1
- For patients already on thyroid hormone replacement, maintaining TSH within the reference range (0.5-4.5 mIU/L) is the treatment goal 1
- The presence of normal T3 and T4 with elevated TSH is classic for inadequate replacement dosing—the peripheral conversion is maintaining hormone levels, but the thyroid gland itself cannot meet demands 1
Specific Dosing Adjustment
Increase desiccated thyroid by 15-30 mg (equivalent to 12.5-25 mcg levothyroxine increment) 1:
- For elderly patients, use the smaller increment (15 mg) to avoid cardiac complications 1
- If she has cardiac disease or is over 70 years old, start with 15 mg increase and monitor closely 1
- If she is younger than 70 without cardiac disease, 30 mg increment is appropriate 1
Critical Monitoring Protocol
- Recheck TSH and free T4 in 6-8 weeks after dose adjustment—this represents the time needed to reach steady state 1
- Target TSH: 0.5-4.5 mIU/L with normal free T4 levels 1
- Once stable, monitor TSH every 6-12 months or if symptoms change 1
Important Caveats for Elderly Patients
Avoid overtreatment, which occurs in 14-21% of patients and carries serious risks 1:
- Atrial fibrillation risk increases 3-5 fold with TSH suppression below 0.45 mIU/L, especially in patients over 60 1
- Osteoporosis and fracture risk increases significantly in elderly women with chronic TSH suppression 1
- Cardiac complications including abnormal cardiac output and ventricular hypertrophy can occur with excessive dosing 1
Why Not Leaving It Alone Is Wrong
Some older studies suggested TSH alone isn't adequate for monitoring 2, but current guidelines uniformly recommend normalizing TSH in patients on replacement therapy 1. Persistent TSH elevation above 4.5 mIU/L, even with normal peripheral hormones, indicates:
- Approximately 5% annual risk of progression to overt hypothyroidism 1
- Potential cardiovascular dysfunction from inadequate tissue thyroid hormone delivery 1
- Adverse effects on lipid metabolism and quality of life 1
Common Pitfall to Avoid
Do not adjust doses more frequently than every 6-8 weeks—levothyroxine (and desiccated thyroid) has a long half-life, and premature dose changes before reaching steady state lead to inappropriate adjustments 1. If TSH remains elevated after 6-8 weeks on the increased dose, make another 15-30 mg increment 1.