Initial evaluation of thyroid dysfunction - Are simultaneous TSH and fT4 tests necessary?

Schneider, Claudio; Feller, Martin; Bauer, Douglas C; Collet, Tinh-Hai; da Costa, Bruno R; Auer, Reto; Peeters, Robin P; Brown, Suzanne J; Bremner, Alexandra P; O'Leary, Peter C; Feddema, Peter; Leedman, Peter J; Aujesky, Drahomir; Walsh, John P; Rodondi, Nicolas (2018). Initial evaluation of thyroid dysfunction - Are simultaneous TSH and fT4 tests necessary? PLoS ONE, 13(4), e0196631. Public Library of Science 10.1371/journal.pone.0196631

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OBJECTIVE

Guidelines for thyroid function evaluation recommend testing TSH first, then assessing fT4 only if TSH is out of the reference range (two-step), but many clinicians initially request both TSH and fT4 (one-step). Given limitations of previous studies, we aimed to compare the two-step with the one-step approach in an unselected community-dwelling study population, and develop a prediction score based on clinical parameters that could identify at-risk patients for thyroid dysfunction.

DESIGN

Cross-sectional analysis of the population-based Busselton Health Study.

METHODS

We compared the two-step with the one-step approach, focusing on cases that would be missed by the two-step approach, i.e. those with normal TSH, but out-of-range fT4. We used likelihood ratio tests to identify demographic and clinical parameters associated with thyroid dysfunction and developed a clinical prediction score by using a beta-coefficient based scoring method.

RESULTS

Following the two-step approach, 93.0% of all 4471 participants had normal TSH and would not need further testing. The two-step approach would have missed 3.8% of all participants (169 of 4471) with a normal TSH, but a fT4 outside the reference range. In 85% (144 of 169) of these cases, fT4 fell within 2 pmol/l of fT4 reference range limits, consistent with healthy outliers. The clinical prediction score that performed best excluded only 22.5% of participants from TSH testing.

CONCLUSION

The two-step approach may avoid measuring fT4 in as many as 93% of individuals with a very small risk of missing thyroid dysfunction. Our findings do not support the simultaneous initial measurement of both TSH and fT4.

Interest & Impact

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5 Citations in Web of Science ®
6 Citations in Scopus

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