Thyroxine Triiodothyronine And Tsh Levels
The main job of the thyroid gland is to make the hormone thyroxine, also known as T4 because it has four iodine molecules. The thyroid also makes the hormone triiodothyronine, known as T3 because it has three iodine molecules, but in smaller amounts, explains Cathy Doria-Medina, MD, an endocrinologist with HealthCare Partners Medical Group in Torrance, California. The thyroid gland makes mostly T4, the T4 has to be converted to T3, because T3 is the part of thyroxine that actually does the work, she says.
The pituitary gland at the base of the brain controls hormone production in your body. It makes thyroid-stimulating hormone , which tells the thyroid gland how much T4 and T3 to produce. The TSH level in your blood reveals how much T4 your pituitary gland is asking your thyroid gland to make. If your TSH levels are abnormally high, it could mean you have an underactive thyroid, or hypothyroidism. Thats because it indicates your pituitary gland is producing more TSH in an effort to stimulate your thyroid to produce thyroid hormone, according to the Mayo Clinic.
TSH levels go in the opposite direction of your thyroid hormone, Dr. Doria-Medina explains. If youre making too little thyroid hormone, your TSH will go up. If youre making too much thyroid hormone, your TSH will go down.
If your TSH is higher than 4.0 mU/L on repeat tests, you probably have hypothyroidism.
Is There Anything Else I Need To Know About A Thyroxine Test
Thyroid changes can happen during pregnancy. Although it is not common, some women can develop thyroid disease during pregnancy. Hyperthyroidism happens in about 0.1% to 0.4% of pregnancies, while hypothyroidism happens in approximately 2.5% of pregnancies.
Hyperthyroidism, and less often, hypothyroidism, may remain after pregnancy. If you develop a thyroid condition during pregnancy, your health care provider will monitor your condition after your baby is born. Also, if you have a history of thyroid disease, be sure to talk with your health care provider if you are pregnant or are thinking of becoming pregnant.
What Can A Thyroid Test Detect
- What Can a Thyroid Test Detect?
When most people hear about the thyroid, they associate it with the inability to lose or gain weight, but it is responsible for much more than that.
In fact, hormones made by the thyroid can impact how quickly your heart beats, how deep you breathe, your body temperature, womens menstrual cycles and cholesterol levels.
Unfortunately, more than 12 percent of people will deal with a thyroid problem in their life, with women being more likely to deal with this issue than men.
Heres what you need to know about the thyroid and what a test can detect.
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Is There Anything Else I Should Know
In the past, panels of tests were more common. More recently, however, the practice has been to order, where possible, one initial or screening test and then follow up with additional testing, if needed, to reduce the number of unnecessary tests. With thyroid testing, one strategy is to screen with a TSH test and then order additional tests if the results are abnormal or if clinical suspicions warrant.
Your thyroid hormone test results can be affected by:
- Increases, decreases, and changes in the proteins that bind T4 and T3
Side Effects And Aftercare
A blood draw is a routine, minimally invasive procedure. During the days immediately after the blood draw, you may notice slight bruising or soreness at the area where the needle was inserted. An ice pack or 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 Are Thyroid Function Tests Used For
People with some conditions have an increased risk of thyroid problems and so are often advised to have thyroid function tests undertaken each year. This conditions include:
Thyroid function tests can also be done to:
- Monitor treatment with thyroid replacement medicine for people who have hypothyroidism.
- Check thyroid gland function in people who are being treated for hyperthyroidism.
- Screen newborn babies for inherited problems with the thyroid gland.
How Are Thyroid Tests Done
In order to properly test the hormone levels of your thyroid, a blood draw will be performed by your doctor or at a lab.
Prior to the blood draw, you will be asked to sit in a chair, roll up your sleeves and relax while a nurse or technician prepares your arm for the draw.
A band of rubber will be tightly tied around your upper arm to force the veins to swell. This makes it easier for a vein to be found so the needle can be inserted.
Having blood drawn is mostly painless, although it is possible to feel a sharp prick when the needle is inserted. This is typically a very quick sensation.
Once the blood has been fully drawn, the needle will be removed and a small bandage will be placed over your wound.
Before your tests are performed, you should tell your doctor if youre taking any medication or if you may be pregnant. This may alter the results of your test.
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Reason #: Lab Ranges Can Be Tricky
Like mentioned above, a normal TSH range is accepted by the medical community to be from 0.5 to 5.0. If you think about it, its a pretty wide range with a multiplier of 10! To demonstrate an example: Amy might feel good when her TSH is at 0.8 while Marianne might need to be at 1.8 to feel like herself. If Amys TSH was 1.8 she would start feeling hypo and possibly put on weight, experience fatigue and foggy brain. If Mariannes TSH was 0.8, she could start feeling hyper and experience heart palpitations, anxiety, problems feeling asleep, etc.
What Do My Thyroid Test Results Mean
The two most common types of thyroid function tests are the T4 and TSH test. Typically, these two tests are ordered together.
The T4 testmore commonly known as the thyroxine testis used to determine if your thyroid is overactive. If this is the case, you will be diagnosed with hyperthyroidism.
Symptoms of hyperthyroidism include unplanned weight loss, tremors, diarrhea and anxiety.
The TSH test will reveal how much thyroid-stimulating hormone is in your blood. Normal levels range from 0.4 to 4.0 milli-international units of hormone per liter of blood.
If youve been diagnosed with hyperthyroidism and your TSH levels are above 2.0 mIU/L, you are at a heightened risk of developing hypothyroidism, which can result in weight gain, fatigue, depression and weak hair and nails.
If your doctor believes you have hyperthyroidism, he or she may order a T3 test to check for levels of the hormone triiodothyronine.
This hormone level should be within 100-200 nanograms of hormone per deciliter of blood. If your levels are abnormally high, it is possible that you are suffering from an autoimmune disorder called Graves disease.
The final thyroid function test your doctor may order is the T3 resin uptake test. Also known as a T3RU, this blood test will measure the binding capacity of a hormone called thyroxin-binding globulin.
Your doctors office should reach out to you within a matter of days to walk you through the results of your thyroid test.
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Reason #: T3 Hormone Is King
T3, also known as triiodothyronine, is the hormone that our body cells have receptors for. This means that for you to have beautiful hair, healthy nails, optimal gut health, a sharp mind and good mood, you need a sufficient amount of the T3 hormone, not T4.
Interestingly, the T3 hormone is produced from T4 by a metabolic conversion that happens in the gut and the liver. Can you see now how you could have a sufficient T4 hormone but if your T3 is low, you will still be feeling like a zombie?
Oh, and by the way, Synthroid is a synthetic version of T4 this means that you still need to convert it to T3 to feel good.
What Is The Thyroid Gland
The thyroid gland is a butterfly-shaped endocrine gland that is normally located in the lower front of the neck. The thyroids job is to make thyroid hormones, which are secreted into the blood and then carried to every tissue in the body. Thyroid hormones help the body use energy, stay warm and keep the brain, heart, muscles, and other organs working as they should.
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How Should I Prepare For A Thyroid Function Test
For the most part, you do not need to do anything before having this test. However, some medicines may change the result of the thyroid function test.
- Tell your doctor about all prescription and non-prescription medication you take.
- If you are taking thyroid medicines, tell your doctor when you took your last dose. Your doctor may ask that you stop taking thyroid medicines temporarily before having this test.
In People With Thyroid Disease
In people being treated for hypothyroidism, a low TSH level may mean:
- Overmedication with thyroid hormone replacement
- Interactions that cause increased absorption or activity despite an optimal dose of medication
- Central hypothyroidism
In people being treated for hyperthyroidism, a low TSH level usually means that further treatment is needed to reduce thyroid hormone levels.
It could also mean that a person must continue to be monitored to make sure thyroid hormone levels return to normal. This is often the case for people who have temporary thyroiditis related to pregnancy or chemotherapy treatment.
Treatment may need to be more aggressive
Medication may not be absorbing enough
Treatment may be more aggressive than needed
Medication may be absorbing too much
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When Should I Get A Tsh Test
TSH is often the first test doctors order when they suspect a patient has a thyroid disorder. Both hypothyroidism and hyperthyroidism are common disorders. All patients with symptoms of these thyroid disorders should have their TSH checked.
If you are having symptoms of these disorders, your doctor may order a TSH or a thyroid panel test. Symptoms of hypothyroidism include:
- Rapid or irregular heartbeat
- Loose, frequent bowel movements
TSH is also used to evaluate patients who are suspected to have other thyroid disorders, such as goiter, thyroid nodule, thyroid cancer, Graves disease, or Hashimotos thyroiditis. These disorders can cause hypothyroidism or hyperthyroidism.
Screening with TSH for hypothyroidism in adults is controversial. Screening means testing in the absence of symptoms. It is most beneficial when early detection and treatment of disease helps people avoid subsequent medical problems. Some organizations, such as the American Association of Clinical Endocrinology, the American Thyroid Association, and the Endocrine Society, favor routine screening for thyroid problems in adults without symptoms.
Because thyroid disorders can complicate pregnancy, screening with a TSH test during pregnancy is recommended for some women. Pregnant women without symptoms of thyroid problems may be screened if they:
Are Test Results Accurate
Although no test is 100% correct all the time, your TSH test is likely to reflect your level of thyroid-stimulating hormone accurately. Most labs now use a highly precise, third-generation testing process for TSH. This method of testing is accurate to within 0.01 mIU/L. Some labs use an older, second-generation testing method, which is accurate to within 0.1 mIU/L.
It is important to bear in mind that thyroid tests are a snapshot of what is going on in your body at the moment the test sample is taken. Your TSH levels may fluctuate based on factors discussed above, such as pregnancy, illness, and age.
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What Other Tests May Be Ordered In Addition To A Thyroid Panel
Blood tests that may be performed in addition to a thyroid panel may include:
- Thyroid antibodies – to help diagnose autoimmune thyroid disease and distinguish it from other thyroid conditions
- Calcitonin – to help diagnose C-cell hyperplasia and medullary thyroid cancer
- Thyroglobulin – primarily to monitor treatment and recurrence of thyroid cancer
- Thyroxine-binding globulin – to evaluate patients with abnormal T4 and T3 levels
Why Every Thyroid Patient Needs To Get Reverse T3 Tested
I consider reverse T3 to be one of the most important thyroid lab tests available because of the information it gives you about thyroid conversion.
Thyroid conversion is a process going on in your body at ALL times and it’s the process your body uses to activate thyroid hormone.
This process is separate and different from the process of TSH production which is what most doctors focus on.
To get a clear picture of thyroid function in your body you need to get all of the available thyroid lab tests.
It’s both possible, and likely, for instance, that even though your TSH level is normal, your body may still have problems converting T4 into T3.
If reverse T3 levels build up in your body, then it doesn’t matter how much free T3 is available.
Reverse T3 will act to block that free T3 and it will prevent your body from feeling better.
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Is The Thyroglobulin Test Suggested For Pregnant Women
Generally, there is a steady increase in the thyroglobulin level during pregnancy. The mothers who had been a thyroid cancer survivor are always recommended to undergo the thyroglobulin test. The test helps in constant monitoring and assessment of the condition of the thyroid cancer by measuring the thyroglobulin levels in the blood.
How Do I Know If My Thyroid Dose Is Correct
Monitoring thyroid levels on medication Correct dosing of thyroid hormone is usually assessed using the same tests for diagnosis of thyroid disease, including TSH and FT4. Thyroid tests are typically checked every 4-6 weeks initially and then every 6 to 12 months once stable. In special circumstances, such as pregnancy, a history of thyroid cancer, central hypothyroidism, amiodarone therapy, or use of combination T4 and T3 thyroid hormone replacement, your endocrinologist may check different thyroid tests. Additionally, your endocrinologist will evaluate for symptoms of hyperthyroidism and hypothyroidism and peform a physicial exam.
Women who are pregnant and women who may become pregnant should only be treated with levothyroxine . Only T4 efficiently crosses the placenta to provide thyroid hormone to the developing fetus. Thyroid hormone is critical in early pregnancy for brain development. Normal ranges for thyroid tests in pregnancy are different and change by trimester. Women with thyroid disease in pregnancy or who are considering pregnancy should be under the care of an endocrinologist to guide therapy.
Got Questions About Normal Thyroid Hormone Levels?
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Guidelines For Sample Collection And Processing:
Note: Free T4 can be falsely elevated if the sample is warmed, as heat causes dissociation of T4 from the carrier proteins increasing free T4 concentrations. Special care should be taken when shipping samples in the summer.
How To Read Thyroid Test Results
This article was medically reviewed by Shari Forschen, NP, MA. Shari Forschen is a Registered Nurse at Sanford Health in North Dakota. She received her Family Nurse Practitioner Master’s from the University of North Dakota and has been a nurse since 2003. This article has been viewed 69,845 times.
The thyroid is a butterfly-shaped gland located in the neck that produces thyroid hormone. Thyroid disorders, in which the gland produces too much or too little of the hormone, can influence many functions in your body, from your heart rate to your metabolism. If your doctor thinks you are suffering from an overactive or under-active thyroid, she may order tests. Reading the results can seem like a complex task however, if you have a systematic approach and understand what each test represents, you can determine whether or not you have a thyroid problem and, if so, what the problem is. Remember that only your doctor can diagnose thyroid disease, so make sure you talk with her about the results so you can begin treatment if necessary.
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What Causes Hypothyroidism
Hypothyroidism has several causes. They include
- Hashimoto’s disease, an autoimmune disorder where your immune system attacks your thyroid. This is the most common cause.
- Thyroiditis, inflammation of the thyroid
- Congenital hypothyroidism, hypothyroidism that is present at birth
- Surgical removal of part or all of the thyroid
- Slowed heart rate
- Goiter, an enlarged thyroid that may cause your neck to look swollen. Sometimes it can cause trouble with breathing or swallowing.
Because hypothyroidism develops slowly, many people don’t notice symptoms of the disease for months or even years.
What Is A Tsh Test
TSH stands for thyroid stimulating hormone. A TSH test is a blood test that measures this hormone. The thyroid is a small, butterfly-shaped gland located near your throat. Your thyroid makes hormones that regulate the way your body uses energy. It also plays an important role in regulating your weight, body temperature, muscle strength, and even your mood. TSH is made in a gland in the brain called the pituitary. When thyroid levels in your body are low, the pituitary gland makes more TSH. When thyroid levels are high, the pituitary gland makes less TSH. TSH levels that are too high or too low can indicate your thyroid isn’t working correctly.
Other names: thyrotropin test
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