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How To Read A Thyroid Blood Test Result

Can I Take The Test At Home


At-home thyroid test kits are commercially available without a prescription and measure the same hormones as the traditional thyroid panel.

For at-home testing, you prick your finger to get the necessary blood sample. That sample is then mailed to a laboratory that conducts the thyroid panel and makes the results available to you directly.

While at-home testing can measure thyroid levels, it is generally not a substitute for a test ordered by your doctor. If an at-home test detects abnormal thyroid levels, your doctor will likely recommend a new blood sample and thyroid panel to confirm the results. At-home tests for thyroid labs may not be as accurate as tests done in a laboratory.

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.

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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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 what’s 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 .

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

Basic Thyroid Package Test Results

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Following is a sample of the results of the Basic Thyroid Package blood test. The reference interval indicates the normal ranges and the flag indicates a result outside of those ranges. Both LabCorp and Quest Diagnostics measure T4 levels using micrograms per Liter for their reference ranges.

  • The thyroid stimulating hormone or TSH signals the thyroid to perform its job and burn calories.
    • Low TSH results may indicate hyperthyroidism.
    • Elevated TSH results may indicate hypothyroidism.
  • T3 uptake is used to estimate the amount of TBG in the blood and how much T3 and T4 is available for the body to use.
  • T3 uptake directly affects the T3 and T4 levels.
  • T4 circulates in the blood and influences how other organs and the heart function in the body.
  • Elevated levels of T4 may indicate hyperthyroidism or thyroiditis. Abnormal elevated results may also be caused by too much iodine, high levels of protein in the blood, or too much thyroid medication.
  • Low levels of T4 may indicate hypothyroidism, iodine deficiency, or possible pituitary gland disorder.
  • T7 is a calculated measure of T4 x T3U
  • LabCorp Example

    TSH reference range: 0.450 to 4.500 uIU/mL. Thyroid Panel: Thyroxine : reference range 4.5 to 12.0 ug/dL T3 Uptake: 24-39% Free Thyroxine Index : 1.2 to 4.9.

    Quest Diagnostics Example

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    What Do The Results From My Thyroid Function Test Mean

    Your doctor will discuss the results of your thyroid function test with you.An abnormal TSH usually indicates a deficiency or an excess of thyroid hormones available to your body, but it does not indicate why this is happening. An abnormal TSH result is usually followed by additional testing of FT3 and/or FT4 to investigate the cause.A high TSH result:

    • often means an underactive thyroid gland
    • can also occur if you have an underactive thyroid gland and are receiving too little thyroid hormone medication
    • can indicate in rare cases a problem with your pituitary gland, such as a tumour.

    A low TSH result:

    • can indicate an overactive thyroid gland or damage to your pituitary gland that prevents it from producing TSH
    • can also occur if you have an underactive thyroid gland and are receiving too much thyroid hormone medication.

    What Do These Labs Tell Us

    So now that we understand that thyroid lab tests are not perfect we can begin to talk about why they may be helpful.

    Thyroid lab tests are still a critical part of thyroid evaluation because they can give us important information on the FUNCTION of the thyroid gland.

    And this is important for several reasons:

    The first is that you should consider the function of all tissues in your body on a spectrum instead of like a light switch.

    In the spectrum analogy, you can think about thyroid gland working as a percentage of some total .

    So your thyroid gland may be working at 70% of normal or some other value.

    This should be compared to the light switch analogy in which some people tend to think about the thyroid either working or not.

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    Thyroid Stimulating Immunoglobulin Test Results

    Following are sample results of the Thyroid Stimulating Immunoglobulin blood test. The reference intervals indicate the normal ranges and the flag indicates a result outside of those ranges.

    • High levels of TSI in the blood can indicate the presence of Graves’ disease, which is an autoimmune disorder that affects the thyroid gland. Grave’s disease may lead to or be the cause of hyperthyroidism.
    • TSI levels may also reveal other thyroid disorders such as Hashimoto’s, which is one of the most common causes of hypothyroidism.

    LabCorp Example

    Thyroid Stimulating Immunoglobulin reference range: 0 to 139.

    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.
    • Lithium.
  • Having recently had an X-ray test that uses contrast material.
  • Being pregnant.
    • 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:

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    Understanding Thyroid Labs For Medication Prescriptions And Adjustments

    Thyroid labs, especially TSH, free T3, and free T4, are going to be critical for determining if you need to start, increase, or reduce the dose of your thyroid hormone medications, as well as if youre on the right thyroid medications.

    Some physicians who prescribe thyroid medications will not prescribe a medication unless the TSH is above 10 IU/mL, and will be satisfied when a person who is taking thyroid meds has a TSH under 10 IU/mL. I think this is the reason why many people continue to have fatigue, cold intolerance, difficulty with weight loss, and hair loss despite taking thyroid medications.

    When the TSH is between 2.5 IU/mL and 10 IU/mL, and/or when T3 and T4 are within normal limits, this is known as subclinical hypothyroidism. This means that the thyroid is still able to make enough thyroid hormone, but not without sacrifice. At this point, our thyroid is working overtime, leading to many of the common symptoms of hypothyroidism.

    The thyroid is constantly getting a signal to make more and more hormone, and your body is likely running out of nutrients to make more hormone. This results in additional inflammation to the thyroid, attracting more antibodies and fueling the autoimmune process. As many as 5 percent of people with subclinical hypothyroidism will progress to overt hypothyroidism each year due to this.

    How Tsh Levels Change

    TSH levels are not very intuitive. Why does a high TSH mean you have an underactive thyroid gland? Why do low levels means the gland is overactive?

    Understanding exactly how the thyroid gland works can help.

    Your thyroid gland produces thyroid hormone. When it functions properly, your thyroid is part of a feedback loop with your pituitary gland that involves several actions:

    First, your pituitary gland senses the level of thyroid hormone that is released into the bloodstream.

    Your pituitary then releases the special messenger hormone TSH, which makes the thyroid release more thyroid hormone. From there:

    • If your thyroid doesn’t produce enough thyroid hormone, your pituitary triggers your thyroid to make more.
    • If your thyroid is overactive and producing too much thyroid hormone, your pituitary senses that and slows or shuts down TSH production.

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    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.

    Why The Test Is Performed

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    Your provider may recommend this test if you have signs of a thyroid disorder, including:

    • Abnormal findings of other thyroid blood tests, such as TSH
    • Hypopituitarism
    • Lump or nodule
    • Enlarged or irregular thyroid gland
    • Problems becoming pregnant

    This test is also used to monitor people who are being treated for thyroid problems.

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    How To Read A Thyroid Blood Test

    If youve ever had a thyroid blood test, you may have felt a little confused by the result. Having your thyroid checked via a blood test can give you a lot of information. It can detect if you have an overactive gland, an underactive gland or an autoimmune thyroid disease such as Hashimotos thyroiditis or Graves disease. Some thyroid conditions cannot be diagnosed via a blood test, these include thyroid nodules, thyroid cancer and an enlarged thyroid gland .

    Your doctor may give you a basic thyroid test that only checks one hormone, or you may be given a thorough test. TSH stands for Thyroid Stimulating Hormone. It is made by the pituitary gland in your brain and instructs your thyroid to manufacture hormones. The two thyroid hormones are called T4 and T3.

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    High Tsh And Normal Ft4

    This pattern of results can signify so-called subclinical hypothyroidism. Measurement of antithyroid peroxidase antibody titres is a useful adjunct to help guide decision-making because positivity predicts a higher risk of subsequent progression to overt hypothyroidism. Again, confirmation that the TSH is persistently raised is generally advised, although in certain circumstances T4 replacement can be instituted without delay. LT4 therapy should be particularly considered in: younger patients women who wish to become or who are pregnant patients with positive TPO antibodies or a rising trend in serial TSH levels and the presence of marked hypercholesterolaemia. Raised TSH with normal TH levels is also seen with assay interference and in patients taking exogenous T4, where it might reflect malabsorption, altered metabolism or poor compliance .

    Low Ft4 With Inappropriately Normal Or Low Tsh

    How To Read Your Thyroid Panel Results

    This combination of TFTs is also seen in NTI and resolves with recovery. However, in the absence of a clear alternative diagnosis, central hypothyroidism must be considered and a full pituitary hormone profile, including assessment for secondary hypoadrenalism, is mandatory. T4 therapy in patients with untreated hypocortisolism can be life threatening and failure to recognise a large pituitary mass compressing the optic chiasm can result in irreversible visual loss.

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    Thyroid Hormone Resistance And Also Disorder Of Thyroid Hormone Transport Or Metabolism

    These are conditions that are rare and very difficult to diagnose properly. In these conditions sometimes because of genetic variation your body might become resistant to thyroid hormone. This is similar to what we see in Type II Diabetes where the body becomes resistant to the lin hormone.

    The second condition is where there is a problem with either too high levels of thyroid binding protein or low levels of thyroid-binding protein. The thyroid hormone in the bloodstream is present in the bound form. Thyroid hormone is bound to thyroid binding protein, so if there is a significant difference in the levels of these thyroid-binding proteins it can interfere with optimal levels. Some of this condition is attributable to high cortisol levels and also is estrogen levels .

    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.

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    Remember Certain Foods And Supplements Can Interfere With Synthroid

    Foods containing soy and cottonseed meal can make Synthroid less effective. Walnuts, grapefruit juice, and dietary fiber can also make Synthroid less effective. If you eat any of these on a regular basis, check with your doctor. He or she may need to adjust your dose of Synthroid.

    Some supplements and medications can also interfere with the way Synthroid works. To avoid this, you should take Synthroid 4 hours before or after taking:

    • Iron supplements and multivitamins with iron
    • Calcium supplements or multivitamins with calcium
    • Antacids

    How Much Does The Test Cost

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    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.

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