What the Free T3 Test (FT3) measures
Free T3 (free triiodothyronine) measures the part of the T3 hormone in the blood that is not bound to proteins and is available to act on the body’s cells. T3 is the most active thyroid hormone: most of it is made by converting T4 into T3 in the body’s tissues, and a smaller amount is released directly by the thyroid gland. Most T3 in the blood is carried on proteins, and the amount of those proteins changes in pregnancy, with oestrogen-containing pills and in some illnesses, which can move total T3 without any real change in thyroid function. Measuring the free part avoids much of that effect. Free T3 is mainly useful when an overactive thyroid (hyperthyroidism) is suspected, particularly when TSH is low but free T4 is normal, because in some people T3 rises first. It is less helpful for diagnosing an underactive thyroid, where TSH and free T4 are the main tests. Doctors also use it to follow treatment of an overactive thyroid. Free T3 is usually read together with TSH and free T4 rather than on its own, and severe illness elsewhere in the body can lower it even when the thyroid itself is healthy.
Price: the Free T3 Test (FT3) costs ₹319 at Pure Bliss (MRP ₹400), with the sample collected at our Action Area 2, New Town centre or at your home.
Who this test is for
- Suspected overactive thyroid, especially with a low TSH
- Symptoms such as a fast heartbeat, weight loss, tremor, heat intolerance or anxiety
- Follow-up during treatment for an overactive thyroid
- Doctors reviewing a thyroid result that does not fit the symptoms
How to prepare, the sample, and when to expect the report
Preparation
Fasting is not required. A morning sample is preferred. If you take thyroid medicine, give the sample before your morning dose unless your doctor says otherwise. Stop biotin supplements for 48 hours beforehand, as biotin can distort thyroid hormone results.
Sample
Blood, from a vein in the arm (serum).
Reporting time
Within 24 hours.
Reading the result
Free T3 ranges differ between laboratories and methods, and are different in pregnancy and in children. The value is usually read together with TSH and free T4. Reference ranges differ between laboratories, so your report lists the laboratory’s own range beside each value. A result outside the range does not always mean illness; ask your doctor to explain it.
- Centre or home collection
- NABL-accredited Redcliffe Labs collection centre
- How collection works →
The Free T3 Test (FT3) can be booked at the clinic in Action Area 2 or with a home collection from 7:30 AM. Patients come to us from Action Area 1, Action Area 3, Rajarhat, Chinar Park, Salt Lake Sector V, Sukhobrishti and Eco Park.