Platform
Company
Endocrine & Reproductive
Review status
Currently under review
Pending specialist review and validation.
This test measures the level of thyroid-stimulating hormone (TSH) in your blood. TSH is made by the pituitary gland and tells your thyroid to produce hormones that help control metabolism, energy, temperature, and growth.
Because TSH responds to small changes in thyroid hormone, it is a sensitive marker of how your thyroid system is functioning. Clinicians often order it together with free T4, and sometimes free T3 or thyroid antibodies, to get a full picture. The test uses a standard blood sample and usually does not require fasting.
TSH helps evaluate symptoms such as fatigue, weight change, hair or skin changes, feeling cold or hot, palpitations, anxiety, sleep problems, or changes in bowel habits. It is also used to screen for thyroid problems, to diagnose underactive or overactive thyroid conditions, and to monitor treatment with thyroid medication.
In newborns and children, identifying thyroid problems early supports normal growth and brain development. During pregnancy, healthy thyroid function supports both parent and baby. TSH also helps your clinician assess risks from medications or illnesses that can affect the thyroid and guides safe dosing of thyroid medicines over time.
A higher TSH usually suggests an underactive thyroid, while a lower TSH can suggest an overactive thyroid or effects of thyroid medication. Rarely, pituitary or hypothalamic conditions can make TSH less reliable, so your clinician may look closely at free T4 and your symptoms.
If your result is unexpected, your clinician may repeat the test, review your medications and supplements, or add tests such as free T4, thyroid antibodies, or imaging. Decisions about starting, stopping, or adjusting treatment depend on more than one value and on how you feel, so do not change any medication without medical advice.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
High-dose biotin, often found in hair and nail products, can distort some immunoassay results and make thyroid results look falsely high or low. To reduce interference, stop biotin for at least 2 days before your blood draw, unless your clinician advises otherwise.
TSH follows a daily rhythm and can vary with time of day, sleep, and stress. Try to test at a similar time on repeat checks, and avoid testing during acute stress if possible, so results are easier to compare.
If you take levothyroxine or liothyronine, take your dose after the blood draw when testing in the morning. Recent dose changes or missed doses can shift results for several weeks, so tell your clinician about any changes.
Amiodarone, lithium, glucocorticoids, dopamine, heparin, and severe non-thyroid illness can affect TSH and thyroid hormone levels. Always provide a full medication list and mention recent illnesses or hospitalizations.
Pregnancy changes thyroid physiology, and different reference intervals may be used. Postpartum thyroiditis can temporarily alter results. Tell the lab and your clinician if you are pregnant, recently pregnant, or breastfeeding.
Pituitary or hypothalamic disease can uncouple TSH from thyroid hormone levels, and rare antibody interferences can skew results. If results do not match how you feel, your clinician may repeat testing or use an alternate method.
References