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

• Published in: PloS one 2018-04, Vol.13 (4), p.e0196631-e0196631
• Main Authors: 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
• Format: Article
• Language: English
• Subjects: Biochemistry; Biology and Life Sciences; Data analysis; Demographics; Diabetes; Diagnosis; Endocrinology; Evaluation; Hospitals; Hyperthyroidism; Hypothyroidism; Internal medicine; Laboratories; Likelihood ratio; Medical research; Medicine; Medicine and Health Sciences; Metabolism; Outliers (statistics); Parameter identification; Physical Sciences; Population; Population studies; Primary care; Research and Analysis Methods; Thyroid; Thyroid diseases; Thyroid function tests; Thyroid gland; Thyroid-stimulating hormone; Thyrotropin; Thyroxine
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0196631

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