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What Does A Thyroid Test Show

What Is Free T4 And Bound T4

TSH test explained | Thyroid stimulating hormone test | Thyroid function test | Blood TSH test

T4 stands for thyroxine, one of two hormones your thyroid gland makes. The thyroid is a butterfly-shaped gland in your neck that helps control your body’s growth and energy use. The T4 test measures the amount of T4 in your blood to show whether your thyroid works as well as it should.

You have two kinds of T4 hormone:

  • Free T4 travels around your bloodstream on its own and goes wherever you need it.
  • Bound T4 attaches to proteins to travel through your blood.

A total T4 test measures both free and bound T4. A free T4 test measures only thyroxine that’s not bound to proteins. Many doctors today use the free T4 test because it’s more accurate than the test for bound T4.

The T4 test can also detect problems with your pituitary gland. This gland releases TSH that directs the thyroid to release its hormones.

The information that follows will help you understand why your doctor has asked for a T4 test. It will also help you know what the results might mean in terms of your own health.

Thyroid Levels During Pregnancy

Thyroid hormone levels change during pregnancy. In fact, the ranges considered normal also change throughout pregnancy. What is considered normal may be slightly different depending on the lab where you get your blood test.

Thyroid levels are measured in milliunits per liter and picomoles per liter . A mole is a way to measure large amounts of very small things like atoms and molecules. A picomole is one-trillionth of a mole.

Normal ranges for non-pregnant people are as follows:

  • TSH: 0.5-4.7 mIU/L
  • Free T4 : 8.0-18 pmol/L
  • Free T3 : 2.30-4.2 pmol/L

Normal ranges for pregnant people are different:

First Trimester:

Thyroid Function Blood Test

A GP may arrange for you to have a blood test to check your thyroid hormone levels. This is known as a thyroid function test.

The test checks the levels of:

  • thyroid-stimulating hormone a hormone produced by the pituitary gland which controls the production of thyroid hormones
  • triiodothyronine one of the main thyroid hormones
  • thyroxine another of the main thyroid hormones

Your thyroid hormone levels will be compared to whats normal for a healthy person of your age. A low level of TSH and high levels of T3 and/or T4 usually means you have an overactive thyroid.

Doctors may refer to these measurements as free T3 and T4 .

Whats considered normal varies depending on things such as your age and the exact testing technique used by the laboratory.

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Do You Have Thyroid Symptoms With Normal Lab Results

According to the American Thyroid Association, 12+ percent of the U.S. population will develop a thyroid condition. An estimated 20 million Americans have a thyroid disorder or disease. As many as 60 percent of those affected are unaware of their condition. Women are affected by thyroid disorders more often than men.

If you tell your doctor you are concerned about thyroid problems, he or she will probably order a lab test. But what if the test comes back negative, yet your symptoms persist? Lets say you cant lose weight, always feel tired, and just feel terrible in general. You and your doctor are probably baffled by your normal thyroid blood test results.

Some thyroid problems cause symptoms without showing up on the standard thyroid panel. For example, you may be symptomatic but cant detect the issue because your thyroid labs are in the normal range? If so, you may suffer from a less common thyroid disorder or thyroid-related dysfunction.

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Who Interprets The Results And How Do I Get Them

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A radiologist, a doctor trained to supervise and interpret radiology exams, will analyze the images. The radiologist will send a signed report to the doctor who requested the exam. Your doctor will then share the results with you. In some cases, the radiologist may discuss results with you after the exam.

You may need a follow-up exam. If so, your doctor will explain why. Sometimes a follow-up exam further evaluates a potential issue with more views or a special imaging technique. It may also see if there has been any change in an issue over time. Follow-up exams are often the best way to see if treatment is working or if a problem needs attention.

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Preparing For A Thyroid Scan

Tell your physician about any prescription or over-the-counter medications youre taking. Discuss how they should be used before and during the test.

You may have to discontinue thyroid medication from four to six weeks before your scan. Some heart medications and any medicine containing iodine also may require adjustments.

For any thyroid scan, you may be asked to avoid certain foods that contain iodine for about a week before your procedure. Typically, you shouldnt eat:

  • dairy products
  • phenothiazines
  • tolbutamide

You shouldnt have any other imaging tests that use radioactive iodine for six weeks before your thyroid scan. A few days before your procedure, your doctor may request a blood test to confirm that your thyroid function is still abnormal. Thyroid scans are used as secondary diagnostic tools to other tests, such as blood work. A scan isnt typically used when thyroid functions are normal. An exception to this is when there are nodules or goiters present.

You may have to fast for several hours before your exam. Food can affect the accuracy of the RAIU measurement.

Youll have to remove any jewelry or other metal accessories before the test. These may interfere with the accuracy of the scan.

A doctor who specializes in nuclear imaging will evaluate the images and results of your thyroid scan. Your results will be sent in a report to your doctor.

T3 And T4 Interpretations

  • A normal TSH and normal T4 show a normal thyroid
  • A low TSH and high T4 generally means an overactive thyroid
  • A high TSH and low T4 means an underactive thyroid
  • A low TSH and low T4 mean low thyroid function because of another problem, such as with the pituitary gland or hypothalamus of the brain

A low T3 value with a high TSH value is diagnostic evidence of low thyroid function. By contrast, a low TSH value with a high T3 value is the opposite, and means an overactive thyroid.

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Tsh Levels During Pregnancy

Thyroid hormones can affect brain and nervous system development of the baby, especially during the first trimester. At around 12 weeks, the baby will start to produce thyroid hormones of its own. Until then, the baby is entirely dependent on the transfer of thyroid hormones from the mother.

Both hypothyroidism and hyperthyroidism can occur during pregnancy. You may also have one of these conditions prior to getting pregnant and not know it.

Untreated thyroid disease can cause miscarriage, premature birth, or low birth weight. It can also cause preeclampsia. Having an underactive thyroid during pregnancy can also affect the babys growth and brain development.

Its important to have your TSH levels checked during pregnancy to make sure that both you and your baby remain healthy.

Hormones secreted during pregnancy can affect TSH levels, altering them from your typical numbers.

This chart provides an overview of normal, low, and high TSH levels for pregnant women who are between 18 and 45 years old:

Normal

Having a doctor monitor your thyroid gland and its production of thyroid hormones is the only way to comprehensively determine thyroid health.

The thyroid is one of several glands and structures that make up the bodys endocrine system.

It works in partnership with the pituitary and hypothalamus glands. These glands stimulate the thyroid to secrete two hormones, which are then released into the bloodstream: T4 and T3.

How Do Tsh Values Change With Age

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  • Newborns and childrenTSH and T4 levels are high in newborn babies. As the baby grows, the levels start dropping. T3 increases during the first year of life, but then it starts dropping .
  • AdolescentsTSH and T4 are decreasing and will reach expected adult levels at around 18 years old .
  • AdultsSeveral studies done on more than 10,000 non-diagnosed people show that for a healthy population TSH value is close to 1.5 mIU/L, and is higher in females than in males. 1 in 10 adults under 30 years has TSH higher than 2.5mIU/liter .
  • PregnancyTSH levels rapidly grow during pregnancy. They increase from the average 1.20 mIU/L in the first trimester to 2.12 mIU/L in the second and 3.30 mIU/L in the third trimester. The range of T3 is 1.74.3 nmol/L in second trimester and 0.43.9 nmol/L in third trimester. T4 range is 92.2252.8 nmol/L in second trimester and 108.2219.0 nmol/L in third trimester .
  • 70+4 in 10 people over 80 years have TSH higher than 2.5mIU/liter, and 1 in 10 has TSH higher than 4.5mIU/liter .

Some research suggests that the upper normal TSH reference range in people over 70 years old should be extended to 6.0 mIU/L . A study on more than 15,000 people in Scotland has confirmed that the TSH values should be reconsidered for different age intervals, and especially in people older than 70 years should not be considered out of normal ranges .

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References

1. Carvalho GA, et al. The clinical use of thyroid function tests, 2013

2. Wartofsky L, et al. The evidence for a narrower thyrotropin reference range is compelling, 2005

3. Hollowell JG, et al. Serum TSH, T, and thyroid antibodies in the United States population : National Health and Nutrition Examination Survey , 2002

4. Dunn JT. Guarding our nations thyroid health, 2002

5. Surks MI, et al. Age-specific distribution of serum thyrotropin and antithyroid antibodies in the US population: implications for the prevalence of subclinical hypothyroidism, 2007

6. Fontes R, et al. Reference interval of thyroid stimulating hormone and free thyroxine in a reference population over 60 years old and in very old subjects : comparison to young subjects, 2013

7. Kumar A, et al. Thyroid function tests in pregnancy, 2013

8. Hubner U, et al. Continuous age-dependent reference ranges for thyroid hormones in neonates, infants, children and adolescents established using the ADVIA Centaur Analyzer, 2002

9. Lewandowsky K. Reference ranges for TSH and thyroid hormones, 2015

10. Vadiveloo T, et al. Age- and gender-specific TSH reference intervals in people with no obvious thyroid disease in Tayside, Scotland: the Thyroid Epidemiology, Audit, and Research Study , 2013

Illness And Thyroid Test Results

Certain illnesses can temporarily affect thyroid hormone results. Diarrhea can interfere with your medication absorption and may alter your lab results. Infections or a bout of an inflammatory condition such as lupus can also have an effect.

A syndrome called nonthyroidal illness or sick euthyroid syndrome can also affect thyroid function and test results. This is a serious illness that requires hospitalization.

People with this condition have a normal TSH level with a low T4 and T3 level. These changes in thyroid levels are thought to be protective. For that reason, people with this condition do not receive treatment to correct thyroid levels.

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Thyroid Function Test Results Explained

The thyroid usually changes slowly. It hardly ever quickly changes to being overactive or underactive: it usually takes a few weeks at least, or even a few months. If you have a thyroid function test that shows something is wrong, it’s usually worth repeating it in 3-6 weeks. That is because there’s always the chance that your thyroid gland could have gone back to normal by itself.

The second thing to bear in mind about thyroid function tests is that medications, and even herbal remedies or vitamin supplements, can affect the accuracy of thyroid results.

For these two reasons it’s always recommended to have a thyroid function test if it is recommended to you by a doctor, rather than having it done privately or without a doctor suggesting it.

How Does The Thyroid Gland Function

What does the blood test actually tell about your thyroid ...

The major thyroid hormone secreted by the thyroid gland is thyroxine, also called T4 because it contains four iodine atoms. To exert its effects, T4 is converted to triiodothyronine 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. The amount of T4 produced by the thyroid gland is controlled by another hormone, which is made in the pituitary gland located at the base of the brain, called thyroid stimulating hormone . The amount of TSH that the pituitary sends into the bloodstream depends on the amount of T4 that the pituitary sees. If the pituitary sees very little T4, then it produces more TSH to tell the thyroid gland to produce more T4. Once the T4 in the bloodstream goes above a certain level, the pituitarys production of TSH is shut off. In fact, the thyroid and pituitary act in many ways like a heater and a thermostat. When the heater is off and it becomes cold, the thermostat reads the temperature and turns on the heater. When the heat rises to an appropriate level, the thermostat senses this and turns off the heater. Thus, the thyroid and the pituitary, like a heater and thermostat, turn on and off. This is illustrated in the figure below.

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Understanding Thyroid Stimulating Hormone

As mentioned above, the thyroid stimulating hormone is produced by the pituitary gland. It works sort of like the master of the hormones, and rules the production of T3 and T4 from its control center.If you have too much TSH, it might mean that your thyroid gland isnt making enough T3 or T4. Remember, the TSH is supposed to stimulate the thyroid gland but if the gland isnt responding, then youll have too much TSH in your system.If your TSH levels are too low, it may mean that your thyroid gland is making too much thyroid hormone. This excessive thyroid production could actually suppress the TSH.

A word of warning for pregnant women: Its incredibly important that your hormones are balanced in pregnancy, as thyroid stimulating hormone plays a role in the development of a healthy fetus.

How Does A Blood Test For Hyperthyroidism Work

A TSH test for hyperthyroidism evaluates your levels of thyroid-stimulating hormone , and the thyroid hormones T3 and T4 may also be evaluated. Because TSH signals the thyroid gland to produce more thyroid hormones, unusually low levels of TSH can mean that your thyroid is making too many hormones. T3 and T4 measurements can also reveal just how high your thyroid hormone levels are, which can help your healthcare provider decide on a treatment strategy.

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What Does It Mean To Have A Blood Value Out Of Range

Medically accepted averages vary from country to country.

If youve moved around a lot, it can be challenging to determine which countrys averages are applicable to you do the averages from your country of origin apply to you or has your averages changed to fit your new environments averages? Keep this in your mind if you are relocating.

One measurement at one point in time will not tell you much. You should re-test one or two times for accuracy. This way you and your healthcare practitioner can actually get a solid overview of your health.

TSH test is a first step towards the diagnosis of hypothyroidism. However it can be very misleading, as its shown to increase with age and its not an immediate sign of a disease .

The same is true for kids. From birth to late childhood they have high TSH values, which eventually drops as they reach puberty .

What Is A Thyroid Panel

What Thyroid Tests Do You Need To Get?

Thyroid function is tested through a series of tests called a thyroid panel. These tests are designed to measure the natural regulation process of the body.

The thyroid gland controls metabolism, mood, and overall energy levels. A healthy thyroid produces two primary hormones: Thyroxine and triiodothyronine. These hormones are essential for a proper thyroid panel.

Triiodothyronine regulates the bodys heart rate as well as digestive functions and brain development. It is responsible for helping to maintain strong bones and control muscles. This hormone is directly secreted into the bloodstream. Too much triiodothyronine can cause a goitre and weight loss. Menstrual cycles may also become irregular.

Thyroxine is the prohormone of triiodothyronine. It is responsible for activating T3 so it can improve mental health, regulate menstrual cycles, and build a healthy digestive system. The difference between these two hormones is due to the process in which they are delivered. The thyroid gland produces more thyroxine, but delivers less triiodothyronine.

A thyroid test measures the level of hormones that can be found in an individuals bloodstream. These types of tests can detect a variety of disorders including Graves disease, Hashimotos disease, hypothyroidism and hyperthyroidism.

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When To Seek Help

Many thyroid conditions present with a wide-range of vague symptoms. While feeling under the weather is a normal occurrence at some point, long periods of persistent symptoms may be an indication of something more serious.

If you are experiencing lethargy, bulging eyes, depression, hair thinning, tremors, or an enlarged thyroid gland, visiting an endocrinologist can help. Most people have a variety of symptoms and do not exhibit every discomfort.

Medical professionals can help diagnose thyroid complications. By administering a blood test, they can detect hormone irregularities in the body. This is a short test and results are usually ready within one to two weeks. Call us at .

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