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.
What Are The Types Of Thyroid Disorders
Blood tests are used to diagnose hypothyroidism or hyperthyroidism. They do not point to a specific cause. In order to determine a cause of the thyroid abnormality, the doctor will consider the patient’s history, physical examination, and medical condition. Further testing might be used to isolate an underlying cause. These tests might include more blood testing for
- thyroid antibodies,
- ultrasound of the thyroid gland, or
If thyroid cancer is suspected and surgery may be required, your physician may ask for a blood test known as thyroglobulin.
- Thyroglobulin is a protein made only by thyroid cells.
- If the thyroglobulin level at baseline is detectable or elevated it can be used as a tumor marker.
- After a total thyroidectomy for cancer the level should fall to an undetectable range since the cells that make thyroglobulin have been removed.
- If the level remains detectable after surgery, there is a possibility of thyroid tissue elsewhere in the body, and metastatic disease should be considered.
- If the level is undetectable for a period of time after surgery and then starts to climb, a recurrence of the cancer – either at the primary site or elsewhere in the body should be considered.
Magnetic Resonance Imaging Scan
MRI scans use magnets instead of radiation to create detailed cross-sectional images of your body. MRI can be used to look for cancer in the thyroid, or cancer that has spread to nearby or distant parts of the body. But ultrasound is usually the first choice for looking at the thyroid. MRI can provide very detailed images of soft tissues such as the thyroid gland. MRI scans are also very helpful in looking at the brain and spinal cord.
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How Do You Test Tsh Levels
Healthcare providers test TSH levels using a blood test. They take a sample of blood from a vein in your arm and send the sample to a laboratory for testing. You usually dont need to do anything special to prepare for a TSH blood test.
A TSH blood test is usually the first test providers order if youre experiencing symptoms related to thyroid issues.
What Imaging Tests Do Doctors Use To Diagnose And Find The Cause Of Thyroid Disease
Your health care professional may order one or more imaging tests to diagnose and find the cause of thyroid disease. A trained technician usually does these tests in your doctors office, outpatient center, or hospital. A radiologist, a doctor who specializes in medical imaging, reviews the images and sends a report for your health care professional to discuss with you.
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What Blood Tests Do Doctors Use To Check Thyroid Function
Doctors may order one or more blood tests to check your thyroid function. Tests may include thyroid stimulating hormone , T4, T3, and thyroid antibody tests.
For these tests, a health care professional will draw blood from your arm and send it to a lab for testing. Your doctor will talk to you about your test results.
What Happens During The Test
T3 tests usually require no preparation. However, some medications, such as birth control pills, can affect the results. Therefore, a person should inform a doctor of any medications that they are taking before undergoing T3 testing. They may need to stop taking them to ensure the accuracy of the test.
During a T3 test, a healthcare professional will select a vein to take blood from either on the inside of the elbow or the back of the hand and clean the area around it with antiseptic. They may use an elastic band to restrict the blood flow. Then, they will insert a needle into the vein and draw blood into a syringe.
Some people feel a pricking or scratching sensation during blood tests. At this point, if the healthcare professional used an elastic band, they will remove it. When they have collected enough blood, they will remove the needle and apply a cotton ball or bandage.
T3 testing generally does not cause side effects, but there is a slight risk of throbbing, soreness, or mild bruising at the injection site. Some people might also feel lightheaded during or just after the procedure.
You can also consider at-home thyroid test kits to measure T3 and other thyroid hormone levels.
High T3 levels can indicate several conditions, including hyperthyroidism and thyrotoxicosis . In some cases, they can signify thyroid cancer, but this disease does not often cause abnormal T3 levels.
Thyrotoxicosis and thyroid cancer are rare, so hyperthyroidism is more commonly the cause.
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What Happens When Tsh Levels Are Too Low
If you have too little TSH, its most likely that your thyroid gland is making excess thyroid hormone. This condition is called hyperthyroidism, or overactive thyroid. A variety of conditions lead to hyperthyroidism, including Graves’ disease and thyroid nodules. A little over 1% of adults in the United States have hyperthyroidism.
Since thyroid hormone suppresses TSH release, high levels of thyroid hormone can cause lower-than-normal TSH levels. Rarely, issues with your pituitary gland, such as a non-functioning pituitary adenoma, can result in low TSH levels as well as low thyroid hormone levels.
Symptoms of low TSH levels
Low TSH levels are usually a sign of hyperthyroidism. Symptoms of hyperthyroidism include:
If youre experiencing these symptoms, its important to talk to your healthcare provider. Hyperthyroidism is treatable.
What Tests Do Doctors Use If I Have A Thyroid Nodule
If your health care professional finds a nodule or lump in your neck during a physical exam or on thyroid imaging tests, you may have a fine needle aspiration biopsy to see if the lump is cancerous or noncancerous.
For this test, you will lie on an exam table and slightly bend your neck backward. A technician will clean your neck with an antiseptic and may use medicine to numb the area. An endocrinologist who treats people with endocrine gland problems like thyroid disease, or a specially trained radiologist, will place a needle through the skin and use ultrasound to guide the needle to the nodule. Small samples of tissue from the nodule will be sent to a lab for testing. This procedure usually takes less than 30 minutes. Your health care professional will talk with you about the test result when it is available.
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Side Effects Of Thyroid Blood Tests And Care
Thyroid blood tests are performed after a routine blood draw. That’s when blood is drawn from you by a syringe and sent to a lab. This is a safe procedure with few potential side effects.
It’s rare, but some people get nauseous or feel faint when they have blood drawn. Let the medical personnel know immediately if you experience these side effects.
Later, you may notice a small bruise or have some tenderness at the needle insertion site. An over-the-counter pain reliever or an ice pack can help with this.
You should get medical attention if the insertion site is:
These are signs of an infection, which needs to be treated with antibiotics.
What Does Low Thyroid Blood Test Mean
Your thyroid gland produces thyroid hormone. When it operates correctly, your thyroid is part of a feedback loop with your pituitary gland that involves a number of crucial steps.
1. First, your pituitary senses the level of thyroid hormone that the thyroid has actually released into the blood stream.
2. Your pituitary then launches a special messenger hormone, called Thyroid Stimulating Hormone . The role of TSH is to promote the thyroid to release more thyroid hormone.
When your thyroid, for whatever factor health problem, stress, surgery, obstruction, for example doesnt or cannot produce adequate thyroid hormone, your pituitary spots this reduction in thyroid hormone, and it moves into action by making MORE TSH, which then activates your thyroid to make more thyroid hormone. This is the pituitarys effort to return the system to regular and normalize thyroid function.
So, a TSH that is greater than typical recommends a thyroid that is underactive and refraining from doing its task of producing enough thyroid hormone. To generalize, then, HIGHER TSH = UNDERACTIVE THYROID/ HYPOTHYROIDISM.
3. If your thyroid is overactive and producing excessive thyroid hormone due to disease, or taking expensive a dosage of thyroid hormone replacement drugs your pituitary senses that there is excessive thyroid hormone circulating, and slows or shuts down TSH production, so that the thyroid will decrease its production of the hormone.
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Normal Results Depend On Factors Like Male Or Female Sex And Age
If you have undergone a thyroid-stimulating hormone test, it is important to understand what high and low levels mean. Generally speaking, high TSH levels suggest that you have hypothyroidism , while low TSH levels are suggestive of hyperthyroidism .
Generally speaking, TSH values are described as follows:
- Normal: Between 0.4 and 4.0 mU/L
- High: Over 4.5 mU/L
- Low: Under 0.4 mu/L
But, there are exceptions to these interpretations as well as variations as to what a “normal” TSH level is. This is because TSH levels can vary by age, male and female sex, and other factors. In the end, the results need to be interpreted alongside other thyroid function tests to make the correct diagnosis.
This article looks at the causes of high and low TSH levels, what they mean, and the various factors that can influence test results.
What Are Normal Tsh Levels During Pregnancy
Its especially important for people who are pregnant to have healthy amounts of TSH and thyroid hormones to ensure the healthy development of their babies. TSH levels fluctuate throughout pregnancy. In general, normal TSH levels during pregnancy include:
- First trimester : 0.18 2.99 .
- Second trimester: 0.11 3.98 uIU/mL.
- Third trimester: 0.48 4.71 uIU/mL.
Always check your labs reference range on your results report. If you have questions about your results, ask your healthcare provider.
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What Are Thyroid Function Tests
Thyroid function tests are a series of blood tests used to measure how well your thyroid gland is working. Available tests include the T3, T3RU, T4, and TSH.
The thyroid is a small gland located in the lower-front part of your neck. Its responsible for helping regulate many bodily processes, such as metabolism, energy generation, and mood.
The thyroid produces two major hormones: triiodothyronine and thyroxine . If your thyroid gland doesnt produce enough of these hormones, you may experience symptoms such as weight gain, lack of energy, and depression. This condition is called hypothyroidism.
If your thyroid gland produces too many hormones, you may experience weight loss, high levels of anxiety, tremors, and a sense of being on a high. This is called hyperthyroidism.
Typically, a doctor who is concerned about your thyroid hormone levels will order broad screening tests, such as the T4 or the thyroid-stimulating hormone test. If those results come back abnormal, your doctor will order further tests to pinpoint the reason for the problem.
If youre concerned about your thyroid function and dont already have a primary care doctor, you can view doctors in your area through the Healthline FindCare tool.
There are also at-home thyroid function tests available from LetsGetChecked and Everlywell. Healthline has also created a list of best at-home thyroid tests here.
Controversies Over Optimal Tsh
Many non-modifiable factors influence a person’s TSH levels and dictate what a “normal” value is in an individual. This not only includes variations by a person’s biological sex or age but fluctuations that regularly occur during different seasons of the year.
Some experts argue that the upper limit of a normal TSH should be loweraround 2.5 mU/L. The reasoning behind this is that the vast majority of adults without thyroid disease have a TSH value between 0.45 and 4.12 mU/L. This is especially true in younger females.
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How Tsh Levels Change
TSH levels seem counterintuitive. Why does a high TSH mean you have an underactive thyroid gland? And why do low levels mean it’s overactive?
To answer that, you have to know that TSH and thyroid hormones are different things. The thyroid hormones are:
Your body uses thyroid hormones to regulate all kinds of processes. That includes how fast you burn calories, your heart rate, and many other automatic functions.
When thyroid hormones are low, your pituitary makes more TSH. That signals the thyroid to increase production. When levels are high, the pituitary releases less TSH. That signals the thyroid to slow down. This is why high TSH indicates low thyroid function and vice versa.
How Are Tsh Levels Controlled
Multiple hormones and glands in your endocrine system work together to carefully control the level of TSH in your bloodstream through a feedback loop.
To start, your hypothalamus releases thyroid-releasing hormone to trigger the release of thyroid-stimulating hormone by your pituitary gland.
Your pituitary gland is connected to your hypothalamus through a stalk of blood vessels and nerves. This is called the pituitary stalk. Your hypothalamus is the part of your brain that controls functions like blood pressure, heart rate, body temperature and digestion. Through the stalk, your hypothalamus communicates with your pituitary gland and tells it to release certain hormones. In this case, your hypothalamus releases thyroid releasing hormone , which stimulates your anterior pituitary lobe to release TSH. Your hypothalamus can also release somatostatin, another hormone, to inhibit the release of TSH from your anterior pituitary.
TSH then stimulates cells in your thyroid to release thyroxine or T4 and triiodothyronine or T3 into your bloodstream. These two hormones prevent your pituitary gland from producing more TSH if the levels of thyroxine and triiodothyronine are too high, thus completing the cycle. When T4 and T3 levels drop, the cycle starts over again.
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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.
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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Tests For Thyroid Cancer
Thyroid cancer may be diagnosed after a person goes to a doctor because of symptoms, or it might be found during a routine physical exam or other tests. If there is a reason to suspect you might have thyroid cancer, your doctor will use one or more tests to confirm the diagnosis. If cancer is found, other tests might be done to find out more about the cancer.
What Are Thyroid Hormones
The thyroid gland produces hormones that are essential for normal body metabolism. Blood testing is now commonly available to determine the adequacy of the levels of thyroid hormones. These blood tests can define whether the thyroid gland’s hormone production is normal, overactive, or underactive.
The thyroid gland is located in the lower part of the neck, below the Adam’s apple.The gland wraps around the windpipe and has a shape that is similar to a butterfly – formed by two wings and attached by a middle part .
The thyroid gland uses iodine to produce thyroid hormones.
- The two most important thyroid hormones are thyroxine and triiodothyronine , which account for 99.9% and 0.1% of thyroid hormones present in the blood respectively.
- However, the hormone with the most biological activity is T3.
- Once released from the thyroid gland into the blood, a large amount of T4 is converted into T3 – the active hormone that affects the metabolism of cells.
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