Should you recheck Thyroid-Stimulating Hormone (TSH) levels when on desiccated thyroid?

TSH Monitoring for Patients on Desiccated Thyroid

Yes, TSH should be regularly monitored in patients taking desiccated thyroid to ensure proper dosing and avoid complications of both under and overtreatment. 1, 2

Monitoring Protocol for Desiccated Thyroid

• TSH should be rechecked every 6-8 weeks while titrating desiccated thyroid therapy until levels stabilize within the target range 3, 4
• Both TSH and free T4 should be measured (not just TSH alone) to properly assess thyroid function, especially in symptomatic patients 3
• Once the appropriate maintenance dose is established, monitor TSH annually or sooner if symptoms change 3, 4

Concerns with Desiccated Thyroid Therapy

• Desiccated thyroid contains both T4 and T3 in a ratio of approximately 4:1, which differs from the human physiological ratio 5
• Serum T3 frequently rises to supranormal values in the absorption phase with desiccated thyroid, which can be associated with palpitations and thyrotoxic symptoms 2, 6
• Studies have shown that therapy with desiccated thyroid causes supraphysiologic elevations in T3 concentration in most patients 6, 7
• Elevated T3 levels may have undesirable effects in some patients, including thyrotoxic symptoms 6

Risks of Inadequate Monitoring

• About 25% of patients on thyroid replacement are unintentionally maintained on doses sufficient to fully suppress TSH, highlighting the importance of regular monitoring 3
• Prolonged TSH suppression increases risk for atrial fibrillation, cardiac arrhythmias, and bone demineralization, particularly in elderly patients 1, 3
• Low TSH values (≤0.1 mU/L) carry a risk of development of atrial fibrillation and are associated with bone loss 2

Special Considerations

• For patients with atrial fibrillation, cardiac disease, or other serious medical conditions, more frequent monitoring may be warranted - consider repeating testing within 2 weeks of dose adjustment 3, 4
• For elderly patients (>70 years), more cautious monitoring is recommended due to increased sensitivity to thyroid hormone and higher risk of adverse effects 3
• When switching from desiccated thyroid to levothyroxine, laboratory values should be rechecked ≥4 weeks following the switch 8

Interpreting TSH Results on Desiccated Thyroid

• If TSH is suppressed (<0.1 mIU/L), the desiccated thyroid dose should be reduced to avoid complications of iatrogenic hyperthyroidism 1, 3
• If TSH remains elevated despite therapy, the dose may need to be increased 3
• It is advisable not to allow TSH to fall below 0.2 mU/L to minimize risks 2

Common Pitfalls to Avoid

• Adjusting doses too frequently before reaching steady state (should wait 4-6 weeks between adjustments) 3, 4
• Failing to measure both TSH and free T4, especially in symptomatic patients 3
• Relying solely on TSH without considering T3 levels, which can be elevated with desiccated thyroid even when TSH appears normal 6, 7
• Overlooking symptoms of thyrotoxicosis due to elevated T3 levels from desiccated thyroid 6