Thyroxine (T4) is a thyroid hormone.
A normal free thyroxine index range is between .7 and 1.9 nanograms per deciliter.
In your body, T4 functions in two different forms.
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It’s useful for evaluating thyroid function.
The results of these tests are analyzed together to help with a diagnosis.
The FTI is not itself a separate blood test.
It is calculated from the results of the total T4 test and the T3 resin uptake test.
Instead, the free T4 level is now measured directly.
If this happens to you, tell the person drawing your blood.
Typically, they’ll have you lie down for a while and drink some water.
Be sure to have your insurance card and any written orders your healthcare provider may have given you.
Tell your healthcare provider about any medications you’re taking and whether they could alter your test results.
Timing and Location
The blood draw itself should just take a few minutes.
If you’re getting multiple tests, it could take slightly longer.
Some healthcare provider’s offices will do the blood draw right there, during your appointment.
In that case, it shouldn’t add much time to the length of your appointment.
What to Wear
You should be able to stay in your own clothing for the blood draw.
Wear either short sleeves or long sleeves that can easily be pushed up past your elbow.
Food and Drink
Any time you’re having blood drawn, you want to be well hydrated.
It may help you avoid becoming nauseous.
However, if your healthcare provider is ordering other tests at the same time, some could require fasting.
Laboratory costs for an FTI test can range from $45 to about $130.
A full set of thyroid tests may cost $500 or more.
This is to ensure the right tests are performed on the right people.
If your veins aren’t standing out well, you may be asked to pump your fist.
Blood Draw
Once a good vein is found, the needle will be inserted.
This is generally the most painful part of the test, but remember, it’s only temporary.
Depending on how many tests are ordered, you may need to fill up two or more vials.
After enough blood has been drawn, the insertion site will be bandaged.
If you have any kind of negative reaction, speak up so you could get proper care.
Usually, even with a bad reaction, people are okay after a few minutes.
If you have any problems or questions, contact your healthcare provider’s office.
You shouldn’t have any other lingering effects from a simple blood draw.
It may also lead to additional tests for Graves' disease.
It may lead to further tests for Hashimoto’s thyroiditis.
An abnormal T4 level alone doesn’t usually lead to a diagnosis.
Your healthcare provider will likely analyze it along with T3 and TSH levels.
The free thyroixine index test is typically done alongside other thyroid blood tests including the TSH and T3 tests.
The results of these tests are analyzed together to help your healthcare provider arrive at a diagnosis.
UCLA Health.Normal thyroid hormone levels.
American Thyroid Association.Thyroid function tests.
2016;26(1):1733. doi:10.11613/BM.2016.002
