Biomarker · Hormones
Thyroid-stimulating hormone (TSH)
TSH is the main screening test for thyroid function. Learn what high and low TSH can mean, why it's paired with free T4 and what affects results.
Written by LON6EVITY Editorial Team · Last updated
Overview
TSH is produced by the pituitary gland and tells the thyroid how much thyroid hormone to make. It is usually the first test used to check thyroid function.
Why it matters
Thyroid hormones influence metabolism, heart rate, energy and cholesterol levels. MedlinePlus explains that a high TSH often suggests an underactive thyroid (hypothyroidism) and a low TSH an overactive thyroid (hyperthyroidism).
Interpreting results
TSH is usually interpreted together with free T4 (and sometimes T3). Mildly abnormal TSH with normal free T4 is common and is often rechecked rather than treated immediately.
How the test is performed
A blood sample. Biotin supplements can interfere with some assays — tell your clinician or lab if you take them.
Reference ranges
Reference ranges and targets differ between laboratories, units and guidelines, and depend on age, sex, method and your overall clinical picture. A single result is not a diagnosis — interpret it with a qualified clinician.
Factors that can affect the result
- Biotin supplements
- Pregnancy
- Acute illness
- Thyroid medication
- Time of day
Questions people commonly ask
- Can high cholesterol be caused by the thyroid?
- Hypothyroidism can raise LDL cholesterol, which is why TSH is sometimes checked when cholesterol is high.
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Understand your biomarkers in context
What does this mean for your own health data? Log your results, follow trends over time and bring an organised summary to your next doctor's appointment.
Sources
- TSH (Thyroid-Stimulating Hormone) Test. MedlinePlus, U.S. National Library of Medicine.