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Sensitive thyrotropin and free thyroxine testing in outpatients. Are both necessary?
Archives of Internal Medicine
|November 11, 1996
Summary
For most outpatients, ordering a sensitive thyrotropin (sTSH) test alone is sufficient for thyroid dysfunction screening. Adding a free thyroxine (FT4) test when sTSH is normal rarely changes treatment decisions.
Area of Science:
- Endocrinology
- Clinical Pathology
- Diagnostic Testing
Background:
- Controversy exists regarding optimal thyroid function test selection.
- Some guidelines recommend sensitive thyrotropin (sTSH) and free thyroxine (FT4) tests, while others suggest sTSH alone.
Purpose of the Study:
- To assess the frequency of simultaneous sTSH and FT4 testing.
- To evaluate the discordance rate between sTSH and FT4 results.
- To determine if single thyroid function tests suffice for ruling out dysfunction.
Main Methods:
- Retrospective analysis of adult outpatient sTSH and FT4 tests over six months.
- Classification of results as concordant or discordant when both tests were performed.
- Chart review for patients with normal sTSH and abnormal FT4 results.
Main Results:
- Both sTSH and FT4 tests were ordered together in 48% of cases.
- Concordance between sTSH and FT4 results was 74.3%.
- Abnormal FT4 results with normal sTSH were rare (0.6% low, 1.3% high) and did not alter treatment.
Conclusions:
- Sensitive thyrotropin (sTSH) testing alone is adequate for most outpatient thyroid function screening.
- Routine ordering of free thyroxine (FT4) with normal sTSH is unnecessary and inefficient.
- Adopting an sTSH-alone strategy could halve annual FT4 test utilization.