Thyroid
TSH
TSH is thyroid stimulating hormone. It is made by the pituitary gland to tell the thyroid how hard to work, so it moves in the opposite direction to thyroid hormone levels. That inverse relationship confuses many people reading their own results.
Typical adult reference range
Roughly 0.4 to 4.0, with pregnancy-specific ranges · mIU/L
Ranges vary between laboratories and by age, sex and method. Always read your own result against the range printed on your own report.
What a high result can mean
A high TSH usually means the pituitary is pushing an underactive thyroid to work harder. Symptoms can include tiredness, weight gain, feeling cold, and low mood. It is usually confirmed alongside a free T4 measurement.
What a low result can mean
A low TSH usually means thyroid hormone levels are high enough that the pituitary has eased off, which points toward an overactive thyroid. It can also occur with some medicines and in early pregnancy.
What commonly affects this result
Time of day, as TSH is higher overnight, recent illness, biotin supplements which interfere with many assays, and pregnancy.
Questions worth asking your doctor
- Should we check free T4 alongside this?
- Am I taking biotin, and could it be distorting this result?
- If this is borderline, when should it be repeated?
See what your own results say
Upload your blood test and get a plain English summary of every value on it, with the questions worth raising at your next appointment.
Analyse my resultsThis page explains what a test measures. It is general information, not medical advice, and it cannot tell you what your own result means. Reference ranges differ between laboratories, and results are only meaningful alongside your history, your symptoms and your other results. Always discuss your results with your doctor.