From the Guidelines
Elevated TSH with low FT4 indicates primary hypothyroidism, which requires treatment with levothyroxine (synthetic T4). The management of primary hypothyroidism involves replacing the deficient thyroid hormone with levothyroxine. According to the most recent guidelines, the typical starting dose for adults is 1.6 mcg/kg/day, usually 50-100 mcg daily, taken on an empty stomach 30-60 minutes before breakfast or 3-4 hours after dinner 1.
Key Considerations
- Medication should be taken consistently at the same time each day, avoiding calcium, iron supplements, and certain foods within 4 hours of taking it.
- TSH and FT4 levels should be checked 6-8 weeks after starting treatment to adjust dosing as needed, with the goal of normalizing TSH (typically 0.5-4.5 mIU/L) 1.
- Common symptoms of hypothyroidism include fatigue, cold intolerance, weight gain, dry skin, and constipation, which should improve with proper treatment.
- Regular monitoring is essential as dosage requirements may change over time.
Special Considerations
- For patients without risk factors (i.e., < 70 years old, not frail, and without cardiac disease or multiple comorbidities), full replacement can be estimated using ideal body weight for a dose of approximately 1.6 mcg/kg/d 1.
- For those older than age 70 years and/or frail patients with multiple comorbidities (including cardiac disease), consider titrating up from a lower starting dose of 25-50 mg 1.
- Elevated TSH can be seen in the recovery phase of thyroiditis, and in asymptomatic patients with FT4 that remains in the reference range, it is an option to monitor before treating to determine whether there is recovery to normal within 3-4 weeks 1.
Monitoring and Adjustment
- Development of a low TSH on therapy suggests overtreatment or recovery of thyroid function, and dose should be reduced or discontinued with close follow-up 1.
- TSH and FT4 levels should be monitored regularly to adjust the dose of levothyroxine as needed, with the goal of maintaining TSH levels within the normal range.
From the FDA Drug Label
The general aim of therapy is to normalize the serum TSH level TSH may not normalize in some patients due to in utero hypothyroidism causing a resetting of pituitary-thyroid feedback. Failure of the serum T4 to increase into the upper half of the normal range within 2 weeks of initiation of levothyroxine sodium therapy and/or of the serum TSH to decrease below 20 IU per litre within 4 weeks may indicate the patient is not receiving adequate therapy In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage. In patients on a stable and appropriate replacement dosage, evaluate clinical and biochemical response every 6 to 12 months and whenever there is a change in the patient’s clinical status Secondary and Tertiary Hypothyroidism Monitor serum free-T4 levels and maintain in the upper half of the normal range in these patients
The patient has elevated TSH with low FT4, indicating primary hypothyroidism. The goal of therapy is to normalize serum TSH levels.
- Monitor serum TSH levels after 6 to 8 weeks of any change in dosage.
- Adjust levothyroxine dosage based on clinical response and laboratory parameters to achieve a normal TSH level.
- Evaluate clinical and biochemical response every 6 to 12 months or when there is a change in the patient’s clinical status.
- Maintain serum FT4 levels in the upper half of the normal range for patients with secondary and tertiary hypothyroidism 2
From the Research
Elevated TSH with Low FT4
Elevated thyroid-stimulating hormone (TSH) levels with low free thyroxine (FT4) levels can be an indication of hypothyroidism. The following points summarize the key considerations:
- The condition can be managed with levothyroxine (LT4) therapy, which is a safe and effective means of hormone replacement therapy for hypothyroidism 3.
- Factors that can influence LT4 absorption include ulcerative colitis, coeliac disease, bariatric surgery, Helicobacter pylori infection, food intolerance, gastritis, mineral supplements, dietary fibre, resins, and various drugs 3.
- In cases where TSH levels remain high despite adequate LT4 dose, the physician should review medications, medical history, and serum FT4 levels, and check for acute adrenal insufficiency, heterophilic anti-TSH antibodies, and Helicobacter pylori infection 3.
- Combination therapy with LT4 and liothyronine (LT3) may be considered in some cases, although the evidence for its effectiveness is limited 4, 5, 6.
- The American Thyroid Association, British Thyroid Association, and European Thyroid Association have developed consensus statements to guide the design of future clinical trials of LT4/LT3 combination therapy 5, 6.
- A trial of combination therapy may be indicated in patients who remain symptomatic despite adequate LT4 monotherapy, but this should be undertaken by experienced clinicians with appropriate monitoring for adverse outcomes 7.
Key Considerations
- LT4 absorption can be influenced by various factors, including gastrointestinal disorders and certain medications 3.
- Combination therapy with LT4 and LT3 may be considered in some cases, but the evidence for its effectiveness is limited 4, 5, 6.
- Patients who remain symptomatic despite adequate LT4 monotherapy may be candidates for a trial of combination therapy 7.
- Monitoring of thyroid function, benefits, and adverse effects is vital in the trial setting 7.