If your healthcare provider has ordered a T4 test, you may wonder what it is. Thyroxine is another name for T4, which is one of the two main types of thyroid hormone the thyroid gland makes. The other type is T3.
There are two T4 tests (free and total T4). A T4 test is often run with a T3 and TSH (thyroid stimulating hormone) to assess overall thyroid health and diagnose or monitor thyroid conditions.
Function of T4
The thyroid is a gland in the front of your throat. It makes hormones that regulate various essential functions, such as how your body uses energy, mood, heart rate, digestion, and more.
There are two types of T4:
Free T4: This type of thyroxine is not bound or attached to any other proteins, so it is considered "free." It is an active form of thyroxine that can easily enter tissues in the body where it's needed.
Bound T4: This form of thyroxine is bound to certain proteins in your body. This makes it less readily available for your body to use. Your body uses bound T4 as a backup supply—it stays bound to proteins until your body needs to use it.
The free T4 test, which measures only the active, unbound portion of T4 in the blood, is often preferred. This is because other proteins in the blood that thyroxine binds to, as well as non-thyroid conditions, can affect total T4 levels.
Testing Thyroxine (T4)
Your healthcare provider may order a total T4 test if you have symptoms that could indicate hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid), especially if you have other risk factors. Risk factors include being a female aged 60 or older and having a family history of thyroid disease.
When testing thyroxine levels, your healthcare provider may use the following lab tests:
Free T4 test: This test measures the levels of free T4 in your bloodstream. It is considered the most accurate test for T4.
Total T4 test: This test measures free T4 and bound T4 levels.
There are several ranges for thyroid hormones depending on your age and underlying health conditions. However, for adults, a general range for T4 is considered 5.0 to 12.0μg/dL.
Your healthcare provider may order other tests to assess thyroid function further in addition to those measuring T4. These generally include measuringthyroid-stimulating hormone(TSH) levelsand triiodothyronine (T3).
If your provider suspects the possibility of another underlying cause for your symptoms, they may also order labwork to assess for autoimmune or other conditions.
What Do Low and High Levels Mean?
Low thyroid levels are a condition known as hypothyroidism. High levels are known as hyperthyroidism. Both of these are treatable conditions.
It is not better to have low or high T4, as both low and high T4 carry health risks.
For example, low levels of T4 may indicate an autoimmune condition known as Hashimoto's thyroiditis. High levels can indicate Graves' disease or thyroiditis. If your T4 is too low or too high, your healthcare provider will conduct further testing and work with you to develop a treatment plan.
:max_bytes(150000):strip_icc()/blood-donor-giving-blood-in-a--medical-research-laboratory-1206035081-3b3dbdc399f345ba9526ad4215353c42.jpg "Total Thyroxine (T4) Test: Uses, Side Effects, Results (1)")
Risks of T4 Tests
The T4 and other thyroid tests are performed on blood samples. Taking blood samples is fairly quick, simple, and low-risk for most individuals. The most common risks people face from a blood test are slight pain or mild bruising afterward, which should go away quickly.
Some people, especially those afraid of needles, may experience dizziness, nausea, or ringing in the ears during or immediately following a blood draw.
Most facilities are well equipped to deal with this reaction, which usually involves lying down and drinking some water. If you have a history of adverse reactions, you may want to arrange for someone to drive you to and from the test facility.
Before the test, let the nurse or phlebotomist who is drawing your blood know if you've had bad reactions to blood draws in the past, if you have a bleeding disorder or are taking blood-thinning medications, or if your skin tears or bruises easily.
Before the Test
Blood for T4 and other thyroid tests can generally be drawn at any time of day. 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.
Talk to your healthcare provider about any medications you're taking and whether they could alter your test results.
You may need to take a break from certain medications if your endocrinologist advises. These include:
- Steroids
- Some cancer drugs
- Thyroid medications (unless you're being checked for how effective the medication is)
Other drugs and supplements may also impact results. Discuss any supplements or medications you take with your healthcare provider before testing. Biotin, in particular, can interfere with thyroid tests.
Pregnancy can also affect thyroid hormone levels. So, if you are pregnant or suspect you might be pregnant, share this with your healthcare provider before testing.
Timing and Location
The blood draw itself should just take a few minutes. If you're getting multiple tests, it could take slightly longer. If the blood is being drawn in your healthcare provider's office during an appointment, it should add very little time to the appointment length.
Going to a lab for the test can require a larger time commitment. If you have a scheduled time for your test, be sure to arrive early enough to check in and pay any copays that may be due at the time. If you're anxious about the test, you may also want to give yourself a few minutes to sit calmly and relax.
Labs are often busy, so if you're dropping in, you may want to call ahead of time or aim for a time of day (such as early in the morning) when they tend to be less crowded.
What to Wear
You should be able to stay in your own clothing for the blood draw. Since your arm will need to be exposed, sleeves that are short or can be pushed up easily are best.
In case of a dizzy spell, you may want to wear flat shoes and clothing that's not tight and constricting.
Food and Drink
Any time you have blood drawn, ensure you're well hydrated. That helps your veins keep their shape, which makes it easier to find them and successfully insert the needle.
Since you don't need to fast before a T4 test, it's a good idea to have something in your stomach, which may help avoid any nausea or lightheadedness.
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.
Cost and Health Insurance
Typically, thyroid function tests are covered by insurance when they're deemed medically necessary. If you have any questions, be sure to call your insurance company ahead of time to see what, if any, out-of-pocket expenses you could face..
Your healthcare provider's office, insurance company, and lab should be able to help you determine the cost before you get the tests.
During the Test
Before the blood draw, the nurse or phlebotomist may ask you to confirm certain information such as your name, birth date, healthcare provider ordering the test, and what test you've been sent for. This is to help prevent errors.
Pre-Test
You'll be asked to expose your arm, and the insertion area will be cleaned with alcohol. The person performing the draw will tie a band around your upper arm to trap blood in your veins, which makes it easier to find a good vein and insert the needle. If your veins aren't standing out well, you may be asked to pump your fist.
During the Test
Once a good vein is identified, the needle will be inserted. The band will be released to get the blood flowing again, and the vial attached to the needle will fill up. 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.
Post-Test
Most of the time, you can leave right away after a blood draw. If you have any kind of negative reaction, let someone at the facility know so you can get the proper care. Usually, even with a bad reaction, people are OK after a few minutes.
After the Test
You may have a little soreness and bruising around the site where the needle was inserted, which typically goes away in a short amount of time. If you have any problems or questions, be sure to contact your healthcare provider.
Side Effects
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.
Follow-Up
Once you have the results, your healthcare provider may want you to return to discuss further testing or treatment options, depending on whether a diagnosis has been made.
If you don't hear back about your results promptly or if you don't understand what the results mean, contact your healthcare provider's office. If you are diagnosed with a thyroid disorder, your healthcare provider will help you develop a treatment plan.
Interpreting Results
Thyroid level ranges change with age and health status, such as whether an individual is pregnant. 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 (especially in women) 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.
