Lab test · Endocrinology
Free Thyroxine (Free T4)
Thyroid function
- Blood sample
- No fasting
- Report within 24 hours
- Home collection
What this test is for
Thyroid function
Free T4 measures thyroxine, the main hormone made by the thyroid gland, in its free form. Most thyroxine in the blood is bound to proteins, and only the small unbound part can enter the body's cells and act on them. Free T4 is usually read together with TSH, the pituitary hormone that controls the thyroid, to show whether the thyroid is underactive, overactive or working normally.
Why a doctor may order it
- To check for an underactive thyroid (hypothyroidism) when you have tiredness, weight gain, feeling cold or constipation
- To check for an overactive thyroid (hyperthyroidism) when you have weight loss, a fast heartbeat, sweating or a tremor
- To follow up an abnormal TSH result
- To monitor treatment with thyroid hormone tablets or anti-thyroid medicines
- To check thyroid function before or during pregnancy when your doctor advises it
How to prepare
Fasting: Not needed.
You can eat and drink normally before this test. If you take biotin (often sold for hair, skin and nails), tell your doctor, because high amounts can affect thyroid test results. If you take thyroid medicine, ask your doctor whether to take it before or after the sample on the test day; otherwise keep taking your usual medicines.
At home
- Sample
- Blood sample
- How it works
- A trained collector comes to your home at the booked time and draws a small amount of blood from a vein in your arm, which only takes a few minutes. If TSH or another thyroid test is booked as well, one draw is usually enough for all of them.
- Report
- Within 24 hours of collection.
What the results can mean
Your report shows free T4 next to the laboratory's reference range. A high free T4, usually with a low TSH, can point to an overactive thyroid, while a low free T4 with a high TSH can point to an underactive one. A low free T4 without a raised TSH is less common and may lead your doctor to check the pituitary gland. Pregnancy, serious illness and some medicines can also change the result, so your doctor will interpret it alongside your symptoms and TSH.
What's included
One test: Free Thyroxine (Free T4), from one blood sample.
Related tests
- Thyroid Stimulating Hormone (TSH)Thyroid function৳400
- Free Triiodothyronine (Free T3)Thyroid function৳500
- Free Thyroid Profile (FT3, FT4, TSH)This profile measures three thyroid tests from one blood sample: TSH, the pituitary hormone that controls the thyroid, and the free forms of the two thyroid hormones, T4 and T3.
- Thyroid Peroxidase Antibodies (Anti-TPO)Anti-TPO antibodies are made by the immune system against thyroid peroxidase, an enzyme the thyroid uses to make its hormones.
- Thyroid Function Test (T3, T4, TSH)A thyroid function test measures TSH, the pituitary hormone that controls the thyroid, together with the thyroid hormones T3 and T4.
- TSH Receptor Antibodies (TRAb)Graves' disease (overactive thyroid)৳2,350
Questions people ask
What is the difference between T4 and free T4?
Total T4 measures all the thyroxine in the blood, including the part bound to proteins. Free T4 measures only the unbound, active part, so it is less affected by changes in those proteins, for example in pregnancy.
Why is free T4 usually tested with TSH?
TSH is often the first value to change in a thyroid problem, and free T4 shows how much hormone the thyroid is actually making. Looking at both together helps your doctor tell what kind of problem it is, if any.
What does a low free T4 mean?
A low free T4 often points to an underactive thyroid, especially when TSH is high. Your doctor will look at your symptoms and other results before deciding whether treatment is needed.
Does pregnancy affect free T4?
Yes. Pregnancy changes thyroid hormone levels, and the thyroid has to work harder. Doctors take the stage of pregnancy into account when reading the result.
How much does a Free T4 test cost in Dhaka?
With Mukti Health the price is ৳500, and the sample is collected at your home in Dhaka. You see the price again before you confirm the booking in the Mukti Health app.
Can I do the Free T4 test at home in Dhaka?
Yes. Book it in the Mukti Health app and a trained sample collector comes to your home in Dhaka to take the blood sample. You do not need to go to a laboratory.
How long does the Free T4 report take?
The report is usually ready within 24 hours of the sample being collected.