A T4 (thyroxine) test helps assess overall thyroid health and diagnose or monitor thyroid conditions.
T4 is one of the main types of hormones produced by the thyroid gland.
A T4 test is often run with tests for T3 and TSH (thyroid-stimulating hormone).
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Risk factors include being a female aged 60 or older and having a family history of thyroid disease.
There are several ranges for thyroid hormones depending on your age and underlying health conditions.
However, for adults, ageneral range for T4is considered5.0 to 12.0g/dL.
What Do Low or High Results Mean?
Low thyroid levels are a condition known as hypothyroidism and high levels are known as hyperthyroidism.
Both of these conditions are treatable.
Both low and high T4 can carry health risks.
It doesn’t require fasting (avoiding food) beforehand.
Be sure to have your insurance card and any written orders your healthcare provider may have given you.
You may need to take a break from certain medications if your endocrinologist advises.
These include:
Other drugs and supplements may also impact results.
Pregnancy can also affect thyroid hormone levels.
If you’re getting multiple tests, it could take slightly longer.
Going to a lab for the test can require a larger time commitment.
What to Wear
You should be able to stay in your own clothing for the blood draw.
Food and Drink
Any time you have blood drawn, ensure you’re well hydrated.
If your healthcare provider orders other tests at the same time, however, some could require fasting.
Be sure to follow all of the instructions given by the practitioner and/or the lab performing the test.
This is to help prevent errors.
You’ll be asked to expose your arm, and the insertion area will be cleaned with alcohol.
If your veins aren’t standing out well, you may be asked to pump your fist.
Once a good vein is identified, the needle will be inserted.
Depending on how many tests are ordered, the nurse/phlebotomist may need to change vials one or more times.
After the requisite blood has been drawn, the insertion site will be bandaged.
Most of the time, you’ve got the option to leave right away after a blood draw.
Usually, even with a bad reaction, people are OK after a few minutes.
If you have any problems or questions, be sure to contact your healthcare provider.
If the site is sore, you may want to ice it or take over-the-counter pain medication.
However, a simple blood draw should not have any other lingering effects.
If you are diagnosed with athyroid disorder, your healthcare provider will help you develop a treatment plan.
There are also debates over what are considered normal low and high limits of thyroid hormones.
Your healthcare provider will discuss your results with you and determine if any further testing or action is required.
Summary
Thyroid disorders are common and usually treatable.
Many thyroid diseases can be managed by medication and possibly dietary changes.
Thyroid tests, such as T4 testing and other bloodwork, generally carry little risk.
If you are concerned about your thyroid function, speak to your healthcare provider.
MedlinePlus.Thyroxine (T4) test.
MedlinePlus.Triiodothyronine (T3) tests.
National Institute of Diabetes and Digestive and Kidney Diseases.Hypothyroidism (Underactive Thyroid).
National Institute of Diabetes and Digestive and Kidney Diseases.Hyperthyroidism (Overactive Thyroid).
UCLA Health.Normal thyroid hormone levels.
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Lewandowski K.Reference ranges for TSH and thyroid hormones.Thyroid Research.
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The Journal of Clinical Endocrinology & Metabolism.
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