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.
Blood Test For Thyroid
Available blood test for thyroid includes the T3, T4, and TSH.
The best approach to know the thyroid capacity is to check the TSH level in thyroid test. The low level of TSH in blood test for thyroid indicates that there is excessive production of thyroid hormones whereas higher level of TSH in thyroid test indicates that there is lower production of thyroid hormones .
TSH test is recommended to know the level of production of TSH secreted by the pituitary gland and balances the production of thyroid hormones.
T4 is done to understand if the over production or under production of hormones is due to the imbalance of the pituitary gland or by the gland itself.
T4 is basically present in the blood either bounded to proteins which helps it in entering various tissues which require thyroid hormone or as free T4. Free T4 is most important during thyroid test to understand how the thyroid is working. Combining the results of TSH test with T4 thyroid test helps in precisely deciding how the thyroid gland is working.
Drawing Blood For Thyroid Function Tests
Talk to your doctor about any medications youre taking, and tell your doctor 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 technician or nurse will tie a band of rubber tightly around your upper arm to make the veins swell with blood. Once the technician 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 technician will collect your blood in test tubes and send it to a laboratory for analysis.
When the technician 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. The technician will then place a small bandage over the wound.
You should be able to return to your normal daily activities immediately.
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What Should I Do To Prepare For A Thyroid Function Test
Thyroid function tests usually require very little preparation.
You don’t need to fast before the blood test. And it doesn’t matter if you have taken your thyroid medicine just before the blood test.
Tell your doctor if you are taking any medication, as some medicines can alter the test results and how they are interpreted.
It is also important to mention if you have had any X-ray tests that have used a special contrast dye, as this may contain iodine which can affect the results. Levels of thyroid chemicals also change in pregnancy, so tell your doctor if you are pregnant when the test is taken.
Note: all newborn children have their thyroid function tested as part of the heel prick test which is offered to all babies and undertaken when they are 5 days old. See the separate leaflet called Newborn Baby Screening Tests for more information.;
Thyroid Blood Test Normal Range
- 0-5 days of age: 5.0-18.5 mcg/dL
- 6 days-2 months: 5.4-17.0 mcg/dL
- 3-11 months: 5.7-16.0 mcg/dL
- 11-19 years: 5.9-13.2 mcg/dL
Adult : 4.5-11.7 mcg/dL
- Values of more than 11.7 mcg/dL in adults or more than the age-related cutoffs in children are seen in hyperthyroidism and patients with acute thyroiditis.
- Values below 4.5 mcg/dL in adults or below the age-related cutoffs in children are seen in hypothyroidism, myxedema, cretinism, chronic thyroiditis, and occasionally, subacute thyroiditis.
- Increased total thyroxine is seen in pregnancy and patients who are on estrogen medication. These patients have increased total T4 levels .
- A thyrotropin-releasing hormone stimulation test may be required for certain cases of hyperthyroidism.
Clinical findings are necessary to determine if thyroid-stimulating hormone, TBG, or free T4 testing is needed.
Adult : 80-200 ng/dL
- Age > or =1 year: 2.8-4.4 pg/mL
Normally triiodothyronine circulates tightly bound to thyroxine-binding globulin and albumin. Only 0.3% of the total T3 is unbound ; the free fraction is the active form.
Thyroid stimulating hormone
Thyroid stimulating hormone normal levels:
- 11-19 years: 0.5-4.3 mIU/L
Adults : 0.3-4.2 mIU/L
For diagnostic purposes, the results should always be assessed in conjunction with the patients medical history, clinical examination and other findings.
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Ask A Laboratory Scientist
This form enables patients to ask specific questions about lab tests. Your questions will be answered by a laboratory scientist as part of a voluntary service provided by one of our partners, American Society for Clinical Laboratory Science. Please allow 2-3 business days for an email response from one of the volunteers on the Consumer Information Response Team.
How To Keep Hypothyroidism Under Control
Because youll need to take thyroid medication every day for the rest of your life, even after the right dose is found, your hormone levels will be monitored regularly to be sure that your treatment is working properly. Eventually, most people with hypothyroidism can just be seen yearly by their doctor, Doria-Medina says.
The American Thyroid Association recommends that you keep your TSH within a narrow range of 0.5 to 2.5 mU/L, but dont be alarmed if your test results vary a little. Some variation is normal because your pituitary gland sends out TSH in pulses, not a steady stream. Also, factors like the time of day youre tested can make a difference. TSH levels are likely to be higher at night and lower during the day. Some people, including those who are pregnant or those with a history of thyroid cancer, have different TSH goals. Talk to your doctor about the target TSH range thats right for you.
If you have new or worsening symptoms or your health status changes such as if you become pregnant, go through menopause, or are given another medicine that can interfere with the absorption of your thyroid hormones, such as anticonvulsants, certain antacids, or iron or calcium supplements you should see your doctor and have your blood tested again, even if its ahead of schedule.
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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.
What About Those Already On Thyroid Medications
If youre already on thyroid meds, but still have symptoms, you may need to up your dosage so that your labs fall within the optimal range, which in turn can help you feel better.
Please take a look at my article on TSH for a letter that you can take to your physician if he/she is not familiar with the current optimal reference range. As I mentioned earlier, I personally feel best with a TSH a bit under 1IU/mL, but you may need some trial and error to find your personal best TSH.
Once you establish a dose of medication thats working for you and as long as your symptoms dont change you can test your thyroid hormones every six months.
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How Much Does The Test Cost
The cost of a thyroid panel depends on your insurance coverage and where the test is performed. If ordered by a doctor, insurance normally covers a thyroid panel except for any patient cost-sharing such as copays or deductibles. Check with your health plan and health care provider for specific cost details.
At-home thyroid tests usually cost less than $150, which includes the cost of shipping your blood sample to the lab.
What Is Thyroid Function Test
Thyroid function test is used to check how well your thyroid is working and to find the cause of problems such as hyperthyroidism or hypothyroidism. The thyroid is a small, butterfly-shaped gland in the front of your neck that makes two thyroid hormones: thyroxine and triiodothyronine . Thyroid hormones control how your body uses energy, so they affect nearly every organ in your body, even your heart.
Thyroxine and triiodothyronine circulate almost entirely bound to specific transport proteins, and there are some situations which these proteins could change their level in the blood, producing also changes in the thyroxine and triiodothyronine levels .
The thyroid function test usually includes:
The total T4 and total T3 tests have been used for many years, but they can be affected by the amount of protein available in the blood to bind to the hormone. The free T4 and free T3 tests are not affected by protein levels and are thought by many to be more accurate reflections of thyroid hormone function. In most cases, the free T4 test has replaced that of the total T4 test. However, some professional guidelines recommend the total T3 test, so either total T3 or free T3 test may be used to assess thyroid function.
Thyroid blood tests help health care professionals diagnose thyroid diseases such as:
Your doctor will start with blood tests and may also order imaging tests.
- Increases, decreases, and changes in the proteins that bind T4 and T3
What is reverse T3?
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What Medications Can Affect The Thyroid Panel Tests
Many multivitamins, supplements , and over-the-counter and prescription medications may affect thyroid test results and their use should be discussed with your healthcare practitioner prior to testing. For example, biotin can interfere with some lab tests, so your healthcare practitioner may advise you to refrain from taking biotin or supplements that contain biotin for a few days before having blood drawn for a thyroid panel.
Patterns Of Thyroid Tests Associated With Thyroid Disease
Primary Hypothyroidism A high TSH and low thyroid hormone level can indicate primary hypothyroidism. Primary hypothyroidism occurs when the thyroid gland makes too little thyroid hormone. Symptoms of hypothyroidism can include feeling cold, constipation, weight gain, slowed thinking, and decreased energy. Causes of primary hypothyroidism include:
- Autoimmune thyroid disease, including Hashimoto’s thyroiditis
- Thyroid gland dysfunction due to a medication
- Removal of all or part of the thyroid gland
- Radiation injury to the thyroid
- Excess treatment with anti-thyroid medications
Early or mild hypothyroidism may present as a persistently elevated TSH and a normal FT4 hormone level. This pattern is called subclinical hypothyroidism and your doctor may recommend treatment. Over time, untreated subclinical hypothyroidism can contribute to heart disease.
It is important to remember that normal TSH levels in older individuals are higher than the normal ranges for younger individuals.
Primary Hyperthyroidism A low TSH and a high thyroid hormone level can indicate primary hyperthyroidism. Primary hyperthyroidism occurs when the thyroid gland makes or releases too much thyroid hormone. Symptoms of hyperthyroidism can include tremors, palpitations, restlessness, feeling too warm, frequent bowel movements, disrupted sleep, and unintentional weight loss. Causes of primary hyperthyroidism include:
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What Is The Thyroid
The thyroid is a small gland below the skin and muscles at the front of the neck, at the spot where a bow tie would rest. It makes two types of thyroid hormones: T3 and T4 . It helps the body do many things, such as get energy from food, grow, and go through sexual development.
The pituitary is a pea-sized gland at the bottom of the brain that makes thyroid stimulating hormone . TSH triggers the thyroid to make more thyroid hormone. The pituitary gland and the thyroid gland send messages back and forth to each other about how much hormone to make to keep the levels normal.
Limitations Of The Test
Because this autoantibody is only present in 90% of people with Graves’, a negative test doesn’t automatically rule out the disease. Your healthcare provider will have to rely on the symptoms you report as well as other tests in order to make a diagnosis.
The TRAb test has seen some controversy over how accurate it is. An analysis of research on the subject, though, finds that the science behind the test has come a long way. Now on its third generation, researchers said that better testing has provided a springboard for better, individualized treatment.
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What Affects The Test
Reasons the interpretation of your test may be affected:
- Taking certain medicines, such as:
- Corticosteroids, estrogen, progesterone, or birth control pills.
- Antiseizure medicines such as phenytoin or carbamazepine.
- Heart medicines such as amiodarone or propranolol.
- Thyroid Biopsy.
- Other blood tests are often used to check how well the thyroid gland is working.
- Because false-positive results can occur when testing a newborn for congenital hypothyroidism, the thyroid hormone tests may be repeated a few days after initial testing. If the results are still abnormal and congenital hypothyroidism is suspected, additional testing is done.
- Thyroid-stimulating hormone test measures the amount of TSH in the blood and is considered the most reliable way to find a thyroid problem. If the TSH test is abnormal, other thyroid hormone tests such as a FT3 or FT4 may be done. For more information, see the topic Thyroid-Stimulating Hormone.
- Thyroid antibodies test measures the presence of antibodies against thyroid tissue. Antibodies may mean that you have an autoimmune disease such as Hashimoto’s thyroiditis or Graves’ disease.
- Other tests used to investigate problems with the thyroid gland include:
What Is A Thyroid Function Test
A thyroid function test is a blood test to check the levels of the hormones made by your thyroid gland. The test also checks the level of a hormone made by the pituitary gland in your brain, which acts on your thyroid gland.
The two hormones, thyroxine and thyroid-stimulating hormone , work together and are usually in balance. In a healthy person the brain produces just the right amount of TSH to keep the thyroid gland ticking over. The thyroid gland then produces just the right amount of thyroxine.
This is called a feedback loop: if the thyroid gland makes too much thyroxine it will feed back to the brain to make less TSH. This diagram shows the feedback loop between the thyroid gland in your neck and the pituitary gland in the brain:
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Thyroid Testing: How It Works
Thyroid tests use a blood sample to measure various hormone levels. Thyroid-stimulating hormone , for example, is often measured to indirectly check if your thyroid gland is producing enough thyroid hormones. TSH levels are usually higher than normal if you have an underactive thyroid .
Thyroid function tests can also measure thyroid hormones like thyroxine to provide a better understanding of how low â or how high â your thyroid hormone levels are.
Whats Included In A Full Thyroid Panel
A full thyroid panel usually checks thyroid-stimulating hormone , triiodothyronine , and thyroxine levels. In some cases, a blood test for thyroid function will also check your bloodâs level of TPO antibodies. If you have abnormal thyroid hormone levels, high levels of TPO antibodies can point to an autoimmune thyroid disease as a possible reason for those abnormal levels.
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What Are Normal Thyroid Hormone Levels
The thyroid itself is regulated by another gland that is located in the brain, called the pituitary. In turn, the pituitary is regulated in part by the thyroid and by another gland called the hypothalamus.
The hypothalamus releases a hormone called thyrotropin releasing hormone , which sends a signal to the pituitary to release thyroid stimulating hormone . In turn, TSH sends a signal to the thyroid to release thyroid hormones. If a disruption occurs at any of these levels, a defect in thyroid hormone production may result in a deficiency of thyroid hormone .
Hypothalamus – TRH
Thyroid – T4 and T3
The rate of thyroid hormone production is controlled by the pituitary gland. If there is an insufficient amount of thyroid hormone circulating in the body to allow for normal functioning, the release of TSH is increased by the pituitary gland in an attempt to stimulate more thyroid hormone production. In contrast, when there is an excessive amount of circulating thyroid hormone, TSH levels fall as the pituitary attempts to decrease the production of thyroid hormone.
- In persons with hypothyroidism , there is a continuously decreased level of circulating thyroid hormones.
- In persons with hyperthyroidism , there is a continuously elevated level of circulating thyroid hormones.