Thyroid
TSH
The hormone that controls the thyroid; the first step in finding out whether the thyroid is underactive or overactive.
Everything about this testWhat it measures
TSH (thyroid-stimulating hormone) is made by the pituitary gland and prompts the thyroid to produce thyroid hormone. If the thyroid is underactive, TSH rises; if it is overactive, TSH falls. This makes TSH the most sensitive single measurement of thyroid function.
- Underactive thyroid (hypothyroidism), including at an early stage without symptoms
- Overactive thyroid (hyperthyroidism)
High
A raised TSH usually fits an underactive thyroid. The pituitary gland then makes extra TSH to stimulate the thyroid. A slightly raised value with a normal free T4 is called subclinical hypothyroidism; it often causes no symptoms and sometimes resolves on its own. Symptoms that may go with it: tiredness, feeling cold, weight gain, slowness, dry skin.
Low
A low TSH usually fits an overactive thyroid, or taking too high a dose of thyroid medication. Symptoms that may go with it: restlessness, palpitations, weight loss, trembling, feeling hot. A slightly low value can also be temporary, for example during or after another illness.
Preparation
- Do you take biotin (vitamin B8, often in hair and nail supplements)? Stop at least 2 days before the sample is taken, or 4 days for a high dose.
If your result is abnormal
The GP usually has free T4 measured and repeats the TSH after a few weeks before making a diagnosis or starting treatment.
Reliability
According to the Dutch GP guideline (NHG), TSH is the first and most sensitive test when a thyroid disorder is suspected. A normal TSH virtually rules out a thyroid disorder; an abnormal TSH is not a diagnosis on its own. The GP then has free T4 (and sometimes antibodies) measured and repeats the test after a few weeks, because TSH can be temporarily abnormal.
Limitations
- TSH can be temporarily disturbed by another illness, after a pregnancy, by medicines (including biotin, amiodarone, lithium and corticosteroids) and in the first months after starting or adjusting thyroid medication.
- The value follows a daily rhythm and is highest at night and early in the morning.
- In a rare disorder of the pituitary gland itself, TSH can be normal while the thyroid is still underactive.
How common is this
An underactive thyroid affects about 3 to 4 in 100 adults in the Netherlands, more often women and older people. An overactive thyroid is less common, about 1 in 100. Subclinical abnormalities (only TSH abnormal) are even more common and by no means always have consequences.
Who is this useful for
Useful with symptoms that fit a thyroid disorder (tiredness, weight change, feeling cold or hot, palpitations, mood symptoms), with thyroid conditions in the family, with a known autoimmune disease or after radiotherapy of the neck. Also for monitoring thyroid medication. In adults without symptoms or risk factors, an abnormal result is often a mild or temporary change that needs no treatment.
Downsides and risks
- A slightly abnormal TSH is often temporary; without a repeat measurement this can lead to unnecessary worry or unnecessary treatment.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results