The thyroid is a small, butterfly-shaped gland in the front of your neck. It makes hormones that control how fast your body uses energy. When it works too slowly or too fast, you can feel tired, gain or lose weight, or feel your heart racing. A simple blood test can show how well your thyroid is working.
This guide explains the three main values on a thyroid report: TSH, T3 and T4.
What is TSH?
TSH stands for Thyroid Stimulating Hormone. It is not made by the thyroid itself. It is made by the pituitary gland in the brain. TSH tells the thyroid how much hormone to make.
Think of it like a thermostat. When thyroid hormone in the blood is low, the brain sends more TSH to push the thyroid to work harder. When thyroid hormone is high, the brain sends less TSH.
This is why TSH often moves in the opposite direction to T3 and T4.
What are T3 and T4?
T4 (thyroxine) is the main hormone the thyroid makes. T3 (triiodothyronine) is the more active form. Much of the T3 in your body is made from T4.
Reports may show total T3 and T4, or free T3 (FT3) and free T4 (FT4). Free hormone is the part that is not attached to proteins in the blood and is available for the body to use.
Normal ranges
These are commonly used adult reference ranges. They are only a guide.
- TSH: about 0.4 to 4.5 µIU/mL
- Total T4: about 5 to 12 µg/dL
- Free T4: about 0.8 to 1.8 ng/dL
- Total T3: about 80 to 200 ng/dL
- Free T3: about 2.3 to 4.2 pg/mL
Ranges differ a little from lab to lab, because each lab uses its own machines and methods. Always use the reference range printed on your own report. Ranges may also be different for pregnant women, newborns and older adults.
What does high TSH mean?
A high TSH usually means the brain is asking the thyroid to work harder, because the thyroid is not making enough hormone. This pattern is often seen in hypothyroidism (underactive thyroid).
Common signs of an underactive thyroid include:
- Feeling tired and slow
- Weight gain without clear reason
- Feeling cold more than others
- Dry skin and hair fall
- Constipation
- Heavy or irregular periods
Sometimes TSH is a little high but T4 is normal. Doctors may call this "subclinical" hypothyroidism and may simply repeat the test after some weeks.
What does low TSH mean?
A low TSH usually means there is too much thyroid hormone, so the brain has reduced its signal. This pattern is often seen in hyperthyroidism (overactive thyroid).
Common signs of an overactive thyroid include:
- Weight loss even when eating well
- Fast or uneven heartbeat
- Feeling anxious, nervous or shaky
- Sweating and feeling hot
- Trouble sleeping
- Loose motions
A low TSH can also happen if a person is taking too much thyroid medicine. Only your doctor can decide what your result means for you.
Things that can affect your result
- Time of day: TSH is often a little higher in the early morning.
- Illness: a recent fever or serious illness can change values for a while.
- Medicines and supplements: some medicines and biotin (a hair and skin supplement) can affect results. Tell your doctor what you take.
- Pregnancy: thyroid needs change in pregnancy, and doctors use different targets.
If you already take thyroid medicine, ask your doctor whether to take it before or after the blood sample on test day.
Who should get a thyroid test?
- People with the symptoms listed above
- Women planning pregnancy or who are pregnant
- People with a family history of thyroid problems
- People with diabetes or other long-term conditions, if their doctor advises
- Anyone already on thyroid treatment, for regular follow-up
Frequently asked questions
Do I need to fast for a thyroid test?
Fasting (khali pet) is usually not needed for a thyroid test alone. Many people still give the sample in the morning so results are easier to compare over time. If your thyroid test is part of a package with sugar or cholesterol tests, follow the fasting advice for the package.
Is a TSH of 5 dangerous?
A TSH slightly above the range is common and is not an emergency. Your doctor will look at your T4, symptoms and history, and may repeat the test. Do not start or stop any medicine on your own.
How often should thyroid be checked?
If your thyroid is normal and you have no symptoms, your doctor may suggest checking it every year or as part of a routine checkup. If you are on treatment, your doctor will tell you how often to test.
Book this test
You can book a thyroid profile with home sample collection, online or on WhatsApp. Book a test, see all thyroid and other tests, or check your report values.
This article is for general information only and is not medical advice. Please talk to your doctor about your symptoms and report.
