Best practice management of patients with thyroid disorders is evolving to allow point-of-care testing of thyroid biomarkers, most commonly thyroxine (T4), triiodothyronine (T3), thyrotropin (TSH), thyroglobulin (TG), antibodies to thyroid antigens including TG and thyroid peroxidase (TPO). Central to this process are laboratory test values, which are defined by analyte reference intervals for healthy subjects against which patient samples can be compared. Despite quality assurance processes, there are significant inter- and intra-laboratory differences over time that can limit the application of clinical practice guidelines and create challenges for patients and treating clinicians [ATA, 2019]. Establishment of reference ranges requires sampling of a “normal” population, i.e., a population without thyroid dysfunction. However, non-diagnosed thyroid disease is common (1–3% of the population in iodine-replete areas has hypothyroidism, with much higher prevalence in older persons and in women [Jonklaas, 2019]). This muddies the value of cut-offs for reference ranges for both sub-clinical and overt thyroid disease. For TSH, authoritative guidelines recommend targeting treatment TSH levels to within the lower half of the normal range, but TSH levels are subject to multiple factors that are patient-specific, including concomitant disease, medications, age, gender, ethnicity, time of day and time of year [Razvi, 2019], making one size fits all cut-off values a question for debate. This video presentation is closely linked to one of the podcasts in this 2024 series – TSH: The impact of increasing age and increasing weight, launched on 29 July 2024. It is highly recommended that you listen to both.