Endocrine
Thyroid-Stimulating Hormone (TSH)
TSH is a hormone released by the anterior pituitary gland that signals the thyroid to produce thyroxine (T4) and triiodothyronine (T3). It is the first-line marker of thyroid function because it responds very sensitively to small shifts in circulating thyroid hormone.
Why it is measured
TSH is measured to screen for and monitor underactive and overactive thyroid states and to help titrate thyroid replacement or anti-thyroid therapy. Point-of-care TSH supports faster triage in primary care, pharmacy and remote settings where central laboratory access is limited.
| Typical range | Indicative adult range: roughly 0.4 to 4.0 mIU/L. Some methods report a slightly different interval, for example 0.5 to 5.0 mIU/L. Reference ranges vary by analyser, assay method and population, and differ in pregnancy and at the extremes of age, so always read the range printed for the specific method. |
|---|---|
| Sample | Capillary finger-prick whole blood, venous whole blood, serum or plasma, depending on the device and cartridge used. |
| Turnaround | Approximately 10 to 15 minutes per sample at or near the patient. |
Point of care devices that report it
- Wondfo Finecare FIA Meter Plus (TSH Rapid Quantitative Test, fluorescence immunoassay)
- Qualigen FastPack IP System (TSH chemiluminescent immunoassay)
- Samsung LABGEO IB10 immunoassay analyser (TSH immunoassay)
Questions, answered
Is a point-of-care TSH result equivalent to a central laboratory result?
Studies show good correlation between several point-of-care TSH systems and reference laboratory immunoassays, but they are not numerically identical. Methods are standardised differently, so results near a clinical decision limit may warrant confirmation on the local laboratory platform. Treat the point-of-care result as a screening or monitoring value and interpret it against the range stated for that specific method.
Why is TSH usually checked before free T4 or free T3?
Because the pituitary amplifies small changes in thyroid hormone, TSH moves earlier and more markedly than the thyroid hormones themselves, which makes it the most sensitive single first-line test of thyroid status. Many services use a reflex approach, adding free T4 or free T3 only when TSH falls outside the reference interval. This is general laboratory practice and not guidance for any individual.
Can timing or supplements affect a TSH measurement?
TSH shows a mild diurnal pattern, tending to be higher overnight and in the early morning and lower in the afternoon, so consistent sampling time helps when trending results. High-dose biotin supplements can interfere with some immunoassay formats and produce falsely altered values, so a recent biotin history is useful context. These are operational considerations and not patient-specific advice.