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Appropriate replacement dose of thyroxine in primary hypothyroidism
H Frey1, O Johannesen, H Kapelrud
1Medical Department B, Aker Hospital, Oslo, Norway.
Acta Medica Scandinavica
|January 1, 1987
Summary
An ultrasensitive thyrotropin (TSH) assay revealed that 20% of primary hypothyroidism patients on thyroxine (T4) replacement therapy were overdosed. This highlights the need for sensitive TSH testing to ensure accurate T4 dosage.
Area of Science:
- Endocrinology
- Thyroidology
- Pharmacology
Background:
- Primary hypothyroidism requires lifelong thyroxine (T4) replacement therapy.
- Monitoring T4 therapy is crucial to avoid both undertreatment and overtreatment.
- Current monitoring methods may not accurately reflect optimal T4 dosage.
Purpose of the Study:
- To assess the prevalence of suppressed serum TSH in patients with primary hypothyroidism on T4 replacement therapy.
- To evaluate the utility of serum TSH levels as an endpoint for T4 dosage adjustments.
- To determine the relationship between T4 dosage, age, and TSH levels.
Main Methods:
- Utilized an ultrasensitive thyrotropin (TSH) assay.
- Assessed 65 patients with primary hypothyroidism receiving T4 replacement therapy.
- Measured serum TSH, thyroxine (T4), and triiodothyronine (T3) levels.
Main Results:
- 20% of patients (13 out of 65) exhibited suppressed TSH levels (≤0.1 mIU/l), indicating thyroxine overdose.
- After dose correction, 48 patients achieved normal TSH values.
- The mean T4 replacement dose was 119 micrograms/24 hours, decreasing with age.
- Serum T4 and T3 levels poorly correlated with TSH levels during therapy.
Conclusions:
- Thyroxine overdose is common when using suppressed serum TSH as the sole endpoint for monitoring.
- Ultrasensitive TSH assays are essential for accurate biochemical follow-up of T4 replacement therapy.
- Serum levels of T4 or T3 are unreliable indicators of adequate thyroxine dosage and TSH secretion.