TSH (thyroid stimulating hormone)
What this test measures
TSH is a messenger hormone made by the pituitary gland at the base of the brain. It tells the thyroid gland in the neck how much thyroid hormone to make. When the thyroid makes too little hormone the pituitary sends more TSH, and when it makes too much the TSH falls, so the test is a sensitive read-out of how the thyroid is performing.
Why doctors request it
It is the first-line thyroid test and is one of the most commonly requested blood tests in the UK. Doctors request it for tiredness, weight change, palpitations, low mood, hair loss, irregular periods, and to check the amount of thyroid medicine someone is taking.
What commonly pushes it up
- An underactive thyroid, most often from autoimmune thyroid disease
- Not enough thyroid hormone replacement being taken, or tablets taken with food, iron or calcium
- Recovery from a recent illness
- Some medicines, including lithium and amiodarone
- Time of day, as TSH is higher in the early morning and overnight
- Older age, in the general population
What commonly pushes it down
- An overactive thyroid, including Graves disease and thyroid nodules
- Too much thyroid hormone replacement being taken
- Pregnancy, especially the first three months
- Acute illness and hospital stays
- Steroid medicines and some other drugs
- Pituitary gland problems, which are uncommon
Everyday reasons for a value outside the range
- It can sit a little outside the range after a recent viral illness and settle on its own
- Taking biotin supplements can interfere with the assay on some analysers
- Morning values are higher than afternoon values
- Different laboratories use different assays and ranges
About the sample
No fasting needed, though morning samples run a little higher. Doctors usually repeat a single unexpected value after six to twelve weeks before acting on it. In someone taking levothyroxine the sample is best taken before that day's tablet.
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Read my report freeThis is an educational summary of results you uploaded. It is not medical advice, a diagnosis or a treatment plan, and it does not replace the doctor who requested the test. If you are worried, or a result is marked outside range, discuss it with your doctor. Written and reviewed by a UK consultant physician. Reference ranges vary between laboratories.