✍️ Written by the MedTestBD Editorial Team · Last reviewed: July 2026
What is the Free T4 Test?
The Free T4 test measures the level of free thyroxine — the unbound, active form of the T4 hormone produced by the thyroid gland. Unlike total T4, free T4 is not attached to carrier proteins in the blood, which makes it a more reliable indicator of actual thyroid hormone activity. It is almost always ordered alongside TSH as part of a thyroid function assessment.
Why is the Free T4 Test Done?
- To confirm hypothyroidism when TSH is elevated — a low Free T4 alongside a high TSH confirms an underactive thyroid
- To confirm hyperthyroidism when TSH is suppressed — a high Free T4 alongside a low TSH confirms an overactive thyroid
- To monitor patients on levothyroxine (thyroxine) replacement therapy
- To investigate symptoms like fatigue, weight changes, cold or heat intolerance, palpitations, or hair loss
- To evaluate thyroid function during pregnancy, as normal ranges differ and thyroid disorders are common in pregnant women
Normal Free T4 Levels
| Group | Normal Free T4 Range |
|---|---|
| Adults (general) | 0.8 – 1.8 ng/dL (10 – 23 pmol/L) |
| Pregnancy (trimester-specific) | Slightly lower — use pregnancy-specific reference ranges |
A low Free T4 with a high TSH confirms primary hypothyroidism. A high Free T4 with a low TSH confirms hyperthyroidism. Normal Free T4 with an abnormal TSH may indicate subclinical thyroid disease. Your doctor will always interpret Free T4 alongside TSH for the most accurate assessment.
How to Prepare for the Free T4 Test
- No fasting is required
- If you take thyroid medication (levothyroxine), ask your doctor whether to take it before or after the blood draw — some doctors prefer the sample taken before the morning dose
- Stop biotin supplements at least 24–48 hours before the test if instructed, as they can falsely alter results
- Inform the lab about any steroids, hormone therapy, or iodine-containing medicines you take
Free T4 Test Price in Bangladesh
Free T4 test prices vary between diagnostic centers across Bangladesh. Compare Free T4 test prices on MedTestBD →
⚠️ This information is for general reference only. Always consult a qualified physician before undergoing any medical test.
