Thyroid function testing in outpatients: are both sensitive thyrotropin (sTSH) and free thyroxine (FT4) necessary?

Area of Science:

• Endocrinology
• Clinical Diagnostics

Background:

• Thyroid function testing assays have improved, yet their appropriate use for detecting thyroid dysfunction remains debated.
• The clinical utility of sensitive thyroid stimulating hormone (sTSH) testing in outpatient settings requires further clarification.

Purpose of the Study:

• To determine if a normal sensitive thyroid stimulating hormone (sTSH) test result is adequate to exclude thyroid dysfunction in outpatients.
• To assess the diagnostic value of sTSH in comparison to free thyroxine index (FT4) testing.

Main Methods:

• A retrospective analysis of 1,392 paired sTSH and FT4 test results was conducted over 26 months.
• Results were categorized as concordant or discordant based on whether sTSH and FT4 indicated similar thyroid status (euthyroid, hyperthyroid, hypothyroid).

Main Results:

• A high concordance rate (96.2%) was observed between sTSH and FT4 results.
• Among 1,192 normal sTSH results, only five showed abnormal FT4 levels, indicating a very low likelihood of dysfunction.
• Excluding FT4 tests for normal sTSH results could yield substantial cost savings.

Conclusions:

• A normal sTSH level is highly predictive of normal thyroid function, making it sufficient for screening outpatients.
• Routine ordering of FT4 tests alongside sTSH may be unnecessary, offering opportunities for cost reduction in healthcare.
• sTSH alone is adequate for initial screening of thyroid dysfunction in outpatient settings.