Where thyroid dysfunction is suspected, testing for thyroid hormones may provide useful insights. Two test approaches exist: the one-step test measures thyroid-stimulating hormone (TSH) and other thyroid hormones in a single step, while the two-step approach measures just the TSH to begin with. If the result of the TSH test is outside of the reference range, other thyroid hormones are measured in a second step. Although guidelines recommend a two-step approach, testing is often carried out in a single step. The objective of the report is to evaluate the clinical implications and compare the costs of the two different testing approaches while taking into account ethical, legal, social and organisational issues.
The literature review identified three studies, published between 1990 and 2021, investigating whether the two-step testing approach had failed to diagnose cases of thyroid dysfunction. In a case series of 2,768 blood samples, the one-step approach resulted in inconsistent test results in 5.3% of cases, which would have been missed in a two-step testing procedure. According to the authors of the study, this percentage figure is likely to be lower in daily clinical practice when the patient's medical history and other external factors are taken into consideration. The economic literature review of ten studies showed that thyroid function tests are sometimes carried out unnecessarily or excessively, indicating potential for cost savings. Using the two-step testing approach enabled cost savings compared with the one-step approach. A new model calculation showed that cost savings of approximately CHF 6.1 million would have been possible in 2020. Reflex testing offered the greatest potential for savings. These tests use the blood sample collected for the TSH tests for the second step too, meaning that a second blood sample does not need to be collected.
The report concludes that, from a clinical perspective, using the two-step testing approach carries only a low risk of missing cases of thyroid dysfunction. In terms of costs, the two-step approach represented a cost saving compared with the one-step approach. The reflex testing approach was the most cost-effective. The use of reflex testing or the two-step approach should take into account the consequences of missed or incorrect diagnoses.