Your TSH value says how hard your pituitary is pulling on your thyroid, and that is something different from how much thyroid hormone you have. TSH is the signal your pituitary, a pea-sized gland at the base of your brain, sends to your thyroid to say how much hormone to make. At the laboratory that runs the test the usual range sits between 0.27 and 4.20 mE/L. If your number is above it, your thyroid is probably running slow; below it, and it is probably running fast. That feels back to front, and it is, because TSH is the signal and not the hormone itself. One result is not a diagnosis, so always check the reference value on your own report and let your GP repeat the measurement if it falls just outside the line.
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Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.
Check your own valueThis test measures how much of the hormone TSH is in your blood, in milli-units per litre (mE/L). Your pituitary makes TSH, and through TSH it tells your thyroid how much to produce. Your thyroid then makes T4 and T3, the two hormones that set your pace: your temperature, your heart rate, your digestion and your energy.
Think of a thermostat. If the house gets too cold, the thermostat turns up, and your pituitary works the same way: if it senses too little thyroid hormone, it sends more TSH. That is where the biggest confusion sits, because a high TSH does not mean your thyroid is working too hard but that your pituitary has to push harder because your thyroid makes too little. So a high number means an underactive thyroid, and a low number an overactive one.
So what does TSH mean on a blood test? It is the most sensitive first test for your thyroid, because small changes in thyroid hormone get strongly amplified in it. That is why a problem often shows up before you notice anything.
You do not need to fast. Free T4, the thyroid hormone itself, is usually measured in the same tube.
Most people arrive here with one question: my number is outside the range, so what now? The honest answer is that it is usually not alarming, because a slightly abnormal result is far from always thyroid disease. There are three very ordinary explanations.
The first is the time of day. TSH is highest overnight and lowest in the early afternoon, and the difference within one person is roughly 31 percent across a day; that is enough to land just above or just below a limit. The second is illness: after flu or an infection your value can stay shifted for weeks. The third is a supplement, because biotin from hair and nail pills can distort your result considerably. That is why your GP almost always repeats the measurement, not because something is badly wrong but because one number is too little.
What a result usually means depends on where it sits. Within 0.27 to 4.20 your thyroid is probably just doing its job and no further investigation is needed. Just above the upper limit is often temporary and sometimes an early underactive thyroid; that gets repeated after a few weeks, with free T4. Clearly raised with symptoms fits a thyroid making too little hormone, and you discuss that with your GP. Just below the lower limit is often temporary or the effect of medication, and gets repeated with free T4 and free T3. Very low with palpitations fits an overactive thyroid, and you do not leave that: call your GP.
This is not a diagnosis and not a replacement for your doctor. It helps you understand your result before that conversation.
Pause biotin
RequiredDo you take a supplement with biotin (vitamin B8, common in hair, skin and nail supplements)? Stop it 72 hours before the draw. Biotin interferes with the measurement of these values.
Timing worth knowing
Good to knowIf you repeat this test, pick the same time of day each time so the results compare.
Have your TSH measured if you have symptoms that fit your thyroid. The best known are fatigue that will not lift, feeling cold and weight gain; on the other side sit palpitations, restlessness, sweating and losing weight instead. If your GP saw a borderline result before, repeating is worthwhile too, and if thyroid disease runs in your family a baseline is useful.
The time of day counts. Give blood in the morning if you can, and around the same hour when you repeat it. You do not need to fast.
If you have just been ill, wait a few weeks, because an infection shifts the result and makes it hard to read. If you take thyroid medication and your dose was just changed, wait 6 to 8 weeks, because measuring sooner gives a number that is still moving.
Always request free T4 alongside: TSH alone shows that something is going on, free T4 shows how much. If your doctor suspects an autoimmune cause, anti-TPO, the antibody that points to it, is added.
If your TSH is low, your thyroid is usually making too much hormone and everything runs a notch faster. Your heart pounds or skips, even when you sit still, you sleep worse and feel restless or short-tempered, you sweat sooner and cope badly with heat, and often you lose weight while eating normally. Trembling hands and more frequent toilet trips also occur. Not every low value means an overactive thyroid: too high a dose of thyroid medication gives the same picture, and early in pregnancy a lower value simply belongs there. If you have palpitations with a low result, do not wait and call your GP.
If your TSH is high, your thyroid is usually making too little hormone and everything runs a notch slower. You are tired, even after a good night, you feel cold sooner than the people around you, your skin gets drier, your hair breaks more easily and your bowels slow down. Many people gain weight slowly without anything having changed, and low mood and slower thinking are part of the same picture. With a mildly raised value you often notice nothing at all, because your thyroid hormone itself is then usually still normal; that is called subclinical, it often does not progress, and that is why a result like that gets repeated before anything happens.
Low TSH may indicate hyperthyroidism. Consider thyroid function panel (Free T4, Free T3) and consultation with an endocrinologist.
High TSH indicates hypothyroidism. Consider thyroid hormone replacement therapy and consultation with an endocrinologist.
Low TSH may indicate hyperthyroidism. Consider thyroid function panel (Free T4, Free T3) and consultation with an endocrinologist.
High TSH indicates hypothyroidism. Consider thyroid hormone replacement therapy and consultation with an endocrinologist.
There is no pill or diet that neatly steers your TSH value. What you can do is make sure the measurement is right, and four things genuinely help.
Stop biotin for a few days. It is in almost every hair, skin and nail supplement, often at 5 to 10 milligrams, and it can falsely lower your TSH and falsely raise your free T4, so your result looks like an overactive thyroid while nothing is wrong. Two to three days off is usually enough, and you do not need to stop an ordinary multivitamin.
Give blood at around the same time each time. That matters more than you think, because your value drops over the course of the day.
Do not measure just after flu; wait a few weeks until you have properly recovered.
Tell them which medicines you take. Lithium and amiodarone can disturb your thyroid, and stomach protectors, calcium and iron slow the absorption of thyroid medication.
If you take levothyroxine, take it after the blood draw, and never adjust your own dose based on a test you requested yourself. Discuss that with your GP.
There is no ideal number that fits everyone. At the laboratory that runs the test the usual range runs from 0.27 to 4.20 mE/L, and anywhere inside that is fine. What counts as a good TSH level also depends on your age, and pregnancy and medication shift the picture too. So look at the reference column on your own result.
Usually your thyroid is making too much hormone: your heart runs faster, you sleep worse, you sweat more and you often lose weight. Sometimes it is caused by too high a dose of thyroid medication, and early in pregnancy a lower value is actually normal. If you have palpitations with it, call your GP.
It is the signal from your pituitary to your thyroid. Your pituitary works like a thermostat: if there is too little thyroid hormone, it sends more TSH. So the number mainly says how hard the pulling is, and does not directly say how much hormone you have.
Because one result is too little to conclude anything. Your value varies with the time of day, with a recent infection and with supplements such as biotin. Measuring again after a few weeks shows whether it is genuinely so, and free T4 is usually measured at the same time.
Usually not straight away. A mildly raised value with a normal free T4 is called subclinical; many people notice nothing, and it often does not progress. Your GP looks at your symptoms, your age and the repeat measurement before anything happens.
Better not. Labs use different analysers and different limits, for example 0.4 to 4.0 instead of 0.27 to 4.20, so a normal TSH level is not the same number everywhere. Compare your result with the reference column printed on your own report.
This marker is included in the following test panels.
Measure your TSH to see at a glance how your thyroid is working. No referral needed.
Thyroid panel: TSH, Free T4, and Free T3.
TSH, Free T4, Free T3, and TSH Receptor Antibodies to help assess Graves' disease.
Investigate some common causes of fatigue: CBC, thyroid, iron, vitamins, glucose, and HbA1c.
Articles that explain this value in context.
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Medical policyDoctor's Assessment Included
Every result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
TSH (Thyroid Stimulating Hormone)
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