Drawing Blood For Thyroid Function Tests
Before you get a blood draw to check your thyroid levels, talk with your doctor about any medications youre taking. Also let them know if youre pregnant. Certain medications and being pregnant may influence your test results.
A blood draw, also known as venipuncture, is a procedure performed at a lab or a doctors office. When you arrive for the test, youll be asked to sit in a comfortable chair or lie down on a cot or gurney. If youre wearing long sleeves, youll be asked to roll up one sleeve or to remove your arm from the sleeve.
A healthcare professional, like a technician or nurse, will tie a band of rubber tightly around your upper arm to make the veins swell with blood. Once the healthcare professional has found an appropriate vein, theyll insert a needle under the skin and into the vein.
You may feel a sharp prick when the needle punctures your skin. The healthcare professional will collect your blood in test tubes and send it to a laboratory for analysis.
When the healthcare professional has gathered the amount of blood needed for the tests, theyll withdraw the needle and place pressure on the puncture wound until the bleeding stops. They will then place a small bandage over the wound.
You should be able to return to your typical daily activities immediately.
Who Performs A T3 Test
A healthcare provider called a phlebotomist usually performs blood draws, including those for a T3 blood test, but any healthcare provider who is trained in drawing blood can perform this task. They then send the samples to a lab where a medical laboratory scientist prepares the samples and performs the tests on machines known as analyzers.
How do I prepare for a T3 test?
You usually dont need to do anything special for a T3 blood test. Depending on the reason for the test, you may need to stop taking certain medications or supplements. In any case, your healthcare provider will give you specific instructions.
Preparing For The Tests
You dont need to do anything special to prepare for the thyroid function tests. If a healthcare professional has ordered other blood tests to be taken at the same time, you may need to fast for several hours before the test. They will let you know of any special instructions to follow.
Otherwise, you will not need to follow any specific directions before the test.
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What Does The Test Measure
T3, also called triiodothyronine, is a thyroid hormone that plays a major role in the body. Along with T4, another important thyroid hormone, T3 regulates the bodys metabolism, activates cells, and enables vital organs to function.
Triiodothyronine is referred to as T3 because this hormone has three iodine atoms attached to it. The other major thyroid hormone, thyroxine or T4, has four iodine atoms. Some of the T3 circulating in your body is made in the thyroid. Most of it, however, starts as T4 then is converted in the blood into T3 by the removal of an iodine atom.
More than 99% of the T3 in the body is bound to proteins as it circulates in the bloodstream. A small proportion, known as free T3, is not attached to proteins. Only the free T3 is able to act on cells and stimulate many physical processes. The relationship between bound and free T3 is regulated by the body in a very fine balance to ensure proper body functions.
The total T3 test measures both bound and free T3, while the free T3 test measures only the T3 that is not attached to protein.
T3 measurements are typically used along with other thyroid function tests, like TSH and free and total T4, to evaluate how your thyroid is functioning.
What Is The Purpose Of Tft
You may require a full thyroid function test if you have hyperthyroidism or hypothyroidism symptoms. In addition, this test could be used to determine how well your thyroid medication is functioning.
Hyperthyroidism is a condition characterized by excessive thyroid hormone levels. As a result, weight loss, sweating, a fast heartbeat, and difficulty sleeping can occur.
Hypothyroidism is a disorder that occurs when thyroid hormone levels are abnormally low. As a result, weight gain, weariness, sensitivity to colds, thinning hair, and depression can occur.
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What Is T3 Uptake
Sometimes, you may hear doctors talking about T3 uptake when discussing thyroid testing. What is T3 uptake? The book Clinical Methods says that T3RU test measures the levels of proteins in the blood that carry thyroid hormone.7 T3 uptake can help your doctor interpret the results of T3 and T4 blood tests. The T3RU test is hardly used these days because the TBG and the free T4 blood tests are now available.
Possible Health Risks Of High T3
In the section below, well discuss some potential health risks of high T3 levels in the blood. This is not a comprehensive list. Having high T3 levels does not necessarily mean these health risks will occur. If you have abnormal thyroid hormone levels, speak to your doctor about how they may affect you.
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What Does A High Tsh Mean
What can happen if the TSH level is too high? If a TSH level is too high, it may be a sign of hypothyroidism. Here are some of the symptoms of hypothyroidism:
- Enlarged thyroid
There are two main forms of hypothyroidism, or an underactive thyroid:
Another form of secondary hypothyroidism, which some even call tertiary hypothyroidism, occurs when your hypothalamus releases too little thyrotropin. This issue with the hypothalamus can affect the pituitary gland, which in turn affects the thyroid gland.
What may be causing high TSH? Autoimmune diseases such as Hashimotos, toxin exposure, or even food allergies may be causing high TSH levels, which is due to low thyroid hormone levels and hypothyroidism.
Side Effects And Aftercare
A blood draw is a routine, minimally invasive procedure and doesnt have many side effects.
During the days immediately after the blood draw, you may notice slight bruising or soreness at the area where the needle was inserted. Placing an ice pack on the affected site or taking an over-the-counter pain reliever can help ease your discomfort.
If you experience a great deal of pain, or if the area around the puncture becomes red and swollen, follow up with your doctor immediately. These could be signs of an infection.
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What Is The Tsh Test
The TSH test is a routine blood test that measures the TSH levels in the bloodstream. This is your first step toward diagnosing a possible thyroid disorder.
The TSH normal range is 0.4-4.0 mIU/L.
So, if your test results come back in that range, it indicates that you have a healthy and perfectly functional thyroid gland.
However, if the test results come back less than 0.4 mIU/L or over 4.0 mIU/L, it indicates potent thyroid disorders in the patient. In such cases, your doctor will prescribe further testing of the T3 T4, and TSH normal range before starting the treatment.
The normal range of T3 is 100 to 200 ng/dL, and the normal range of T4 is 5.0 to 12.0 g/dL.
Another marker in the thyroid function test is the free T4 levels. The normal range for that is 0.8 to 1.8 ng/dL.
If your test results for any of these hormones arent in the normal range, it indicates a potent thyroid disorder in the body. Such cases are treated with hormone therapy or assistive treatments as suggested by your doctor.
Alteration Of Thyroid Function Studies In Hypothyroidism
Hypothyroidism most often is caused by glandular hypo-function. T4, T3 RU, free T4 index, free T4, and T3 fall within the normal range or are low . TSH and/or TRHTSH responsiveness are high. When pituitary or hypothalamic disease is at fault, the TSH may be low or normal. TRH-TSH responsiveness will be blunted in the case of pituitary disease or delayed and possibly exaggerated in hypothalamic and pituitary disease.
Thyroid Function Studies in Hypothyroidism.
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What Is Thyroid Hormone
Thyroid hormone is made by the thyroid gland, a butterfly-shaped endocrine gland normally located in the lower front of the neck. Thyroid hormone is released into the blood where it is carried to all the tissues in the body. It helps the body use energy, stay warm and keeps the brain, heart, muscles, and other organs working as they should.
Thyroid hormone exists in two main forms: thyroxine and triiodothyronine . T4 is the primary form of thyroid hormone circulating in the blood . To exert its effects, T4 is converted to T3 by the removal of an iodine atom this occurs mainly in the liver and in certain tissues where T3 acts, such as in the brain. T3 normally accounts for about 5% of thyroid hormone circulating in the blood.
Most thyroid hormone in the blood is bound by protein, while only a small fraction is “free” to enter tissues and have a biologic effect. Thyroid tests may measure total or free hormone levels.
Thyroid Questions Let Us Answer Them
Now you know all about normal thyroid hormone levels and when you need to seek treatment.
PrimeHealth is devoted to answering peoples questions about medical conditions and autoimmune diseases, like Hashimotos thyroiditis. We believe its important to make patients feel heard and educate them on what is going on in their bodies.
Did you know? A lot of peoples hypothyroidism can be permanently cured. Even what conventional doctors might call permanent hypothyroidism may be treatable. Our patients prove it.
To schedule a FREE phone consultation with a member of our medical staff, schedule your appointment today.
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An Overview Of Thyroid Hormones
- TSH: TSH is released from the pituitary gland in the brain. It stimulates the thyroid gland to make thyroid hormones.
- T3 and T4: The thyroid gland makes and releases T4, as well as some T3. Total T3 and T4 levels include T3 and T4 that is bound to protein, as well as T3 and T4 that is not, known as free T3 and free T4.
- T4 conversion to T3 and rT3: After its release from the thyroid gland, T4 is converted to T3, which is an active thyroid hormone, or to rT3, which is considered an inactive form. The rate and ratio of T4 conversion to either T3 or rT3 depend on the bodys metabolic needs.
You can have hyperthyroidism or hypothyroidism due to a problem with any step in the process of thyroid hormone stimulation, production, activation, or protein binding. Your healthcare providers look at these tests to determine which step or steps are responsible for your symptoms.
Laura Porter / Verywell
Tsh And Its Role In Thyroid Function
TSH stands for Thyroid Stimulating Hormone, and is the main hormone checked by doctors to assess thyroid function. TSH is actually secreted by the pituitary gland in the brain, not the thyroid gland.
The pituitary gland will secrete more TSH in response to sensing a need for more thyroid hormone production. TSH then travels to the thyroid gland and, as its name implies, stimulates it to make more thyroid hormone.
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What Is Free T4
Similar to free T3, free thyroxine levels are the unbound levels of T4 hormone . You have more free T4 in your blood than FT3. High T4 levels or low T4 levels can help to accurately diagnose hyperthyroidism or hypothyroidism. The book Clinical Methods says that blood tests for both TSH and T4 help to accurately assess thyroid health.7
The amount of free T4 helps doctors see how much thyroid gland hormone is available in your blood to meet your energy requirements.
Tests For Measuring T4 And T3
The British Thyroid Foundation says that testing for thyroid dysfunction can include one or more of the following tests:6
- Testing to see if free thyroxine is within the range of 0.7 1.8 ng/dL
- Free triiodothyronine tests for the range of 260 480 pg/dL
- TSH and FT4 test
- Testing for thyroid antibodies to diagnose Graves disease or Hashimotos disease
Doctors recommend testing for T4 and T3 as part of a thyroid function test if you have any of the following symptoms:
- Fast or irregular heartbeat
- Thickening around the base of the neck
- High cholesterol
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Does It Even Matter
So, back to the main question:
Does the T3 uptake thyroid lab test even matter?
The short answer is no.
Because you can get more meaningful and direct information when looking at other thyroid lab tests.
The T3 uptake lab test gives you an indirect measure of how well your thyroid-binding protein is working.
But that bound protein isnt useful to you as the patient because it is bound to a protein which makes it unusable.
What you care about instead is the amount of FREE thyroid hormone floating around in your bloodstream.
And you can measure that DIRECTLY with the thyroid lab tests free T3 and free T4.
You can look at both of these free thyroid hormones and get an immediate understanding of how much thyroid hormone is free and available for your body to use.
And this is much more valuable than having some idea as to how much thyroid hormone is probably bound to proteins in your blood.
Exposure To Toxic Metals
Certain heavy metals can be toxic to humans. Cadmium, in particular, can disrupt the bodys balance of thyroid hormones .
Research suggests that exposure to even low levels of cadmium can cause the thyroid gland to become hyperactive and secrete more T3 and T4. Cadmium exposure is also linked to thyroid tumors, which further increase the levels of thyroid hormones .
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Tsh Vs Free T3 Total T3 & Free F4
Like most people, you are probably more familiar with TSH as a marker for testing your thyroid.
And you wouldnt be alone in this understanding because Doctors also love to use this test.
But is it the single best test to assess thyroid function in your body? Did you know that there are many other thyroid function tests?
The answer may surprise you.
It turns out that in healthy individuals TSH is probably a great way to assess thyroid function in the body.
Its also probably the best way to quickly glance at thyroid function, through lab tests, to determine if the thyroid is normal.
But where it fails is when you use it as the only source to help manage patients who are already taking thyroid medication.
We know, from recent studies, that TSH fails to predict free T3 and free T4 levels in patients who are taking thyroid medication.
Thats important, but what exactly does it mean?
It means that if you are taking thyroid medication that you may have a completely normal TSH, but that doesnt mean that your free thyroid hormone levels are normal.
This may explain why many patients on these types of medications dont feel optimal despite having normal thyroid levels.
Thats where free T3 steps in.
Free T3 can, and should, be used in conjunction with the TSH to ensure that you are getting a sufficient amount of ACTIVE thyroid hormone to your cells.
And this way of looking at hormones shouldnt be surprising to you or Doctors.
Well, the TSH is NOT that marker.
What Happens When T3 Levels Are Low
Lower-than-normal T3 levels may indicate you have hypothyroidism . However, healthcare providers dont typically rely on T3 tests to diagnose hypothyroidism because its usually the last of the thyroid function tests to come back abnormal.
In addition, some people can have severe hypothyroidism with a high TSH level and a low free T4 level but have a normal T3 level.
Lower-than-normal T3 levels can also be due to medications like steroids and amiodarone and severe illness. These factors can decrease the amount of T4 your body converts into T3 , resulting in a lower level of T3.
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Treating Hypothyroidism With Replacement T4 And T3
Doctors treat the symptoms of hypothyroidism by prescribing oral thyroid hormone replacement therapy. Some treatments for an underactive thyroid involve prescribing T4 replacements like levothyroxine sodium . Other treatments involve a combination of T4 and T3 replacement therapy.
According to a study in the Journal of Clinical Endocrinology and Metabolism, there is a move towards using combined replacement of T4 and T3 therapies. Some doctors prefer this because the combined T4 and T3 thyroid treatments may have less impact on quality of life and treat hypothyroidism better.23
Strategy For The Diagnosis Of Hyperthyroidism
Hyperthyroidism presents in remarkably diverse ways. On the one hand is the anxious young woman with classic signs and symptoms, while on the other is an elderly male with only goiter and proximal muscle weakness. In the former, a confirmatory test is adequate in the latter, a number of equivocal tests may necessitate protracted follow-up or a therapeutic trial. In either event, it is critical to establish the diagnosis of hyperthyroidism. is intended to offer guidance to the physician seeking to diagnose hyperthyroidism. It will not replace thorough knowledge of the patient, nor can it be a substitute for rigorous thinking.
If the studies are equivocal, a therapeutical trial may be warranted. Time permitting, repeated observations and testing at monthly intervals will often be diagnostic.
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