ft4 (eclia)
ThyroidBlood sampleResults 24 hrsNo fasting
FT4 (ECLIA)
FT4 (Free Thyroxine) measures the active, unbound form of the T4 hormone that is available for your body to use. It is a key thyroid marker, often paired with TSH: low FT4 can suggest an underactive thyroid, while high FT4 can suggest an overactive thyroid.
Sample
Blood
Results
24 hrs
Fasting
Not required
Follow-up
Optional add-on
What this test detects
Free T4 (FT4)
ECLIA · serum
Quantitative (ng/dL)
When to get this test
Suspected hypo- or hyperthyroidism
Helps assess whether the thyroid is underactive or overactive, usually together with TSH.
Clarifying an abnormal TSH
Commonly checked when TSH is high or low to confirm and characterise a thyroid problem.
Fatigue or weight changes
Useful for tiredness, weight changes, neck swelling, or sensitivity to heat or cold.
How to prepare
01
No special preparation needed.
02
If you take thyroid medication, ask whether to take it before or after the draw.
Common questions
Do I need to fast before an FT4 test?
No, fasting is not required. You can eat and drink as usual before your test.
What is the difference between FT4 and TSH?
FT4 measures the active thyroid hormone available in your blood, while TSH is the signal from your pituitary gland that controls the thyroid. Checking both helps identify where a thyroid problem comes from.
How is FT4 different from total T4?
FT4 measures only the free, unbound hormone that your body can actually use, while total T4 also includes hormone bound to blood proteins. FT4 is often preferred for a clearer assessment.