What Are Thyroid Blood Tests And Why Are They Taken
Thyroid blood tests are used to tell if your thyroid gland is functioning properly by measuring the amount of thyroid hormones in your blood. They are done by withdrawing blood from a vein in your arm. These blood tests help to diagnose thyroid diseases.
The thyroid is a butterfly-shaped gland located in the front part of your neck. Its job is to produce thyroid hormones, which travel through your bloodstream and regulate many aspects of your bodys metabolism, including temperature, weight, and energy.
Thyroid blood tests show if you have:
- Hyperthyroidism: Overactive thyroid producing more thyroid hormones than your body needs. Hyperthyroidism speeds up your metabolism, which can cause weight loss, rapid heartbeat, insomnia, puffiness around the eyes, anxiety and other symptoms. The most common cause of hyperthyroidism is Graves disease.
- Hypothyroidism: Underactive thyroid producing too few thyroid hormones. Hypothyroidism slows down your metabolism, which can cause weight gain, menstrual irregularity, dry and puffy skin, fatigue and other symptoms. The most common cause of hypothyroidism is Hashimotos disease.
Thyroid blood tests are used to diagnose thyroid disorders associated with hyper- or hypothyroidism. These include:
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.
This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases, part of the National Institutes of Health. The NIDDK translates and disseminates research findings to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.
The NIDDK would like to thank:COL Henry B. Burch, MD, Chair, Endocrinology Division and Professor of Medicine, Uniformed ServicesUniversity of the Health Sciences
When Tsh Alone Is Not Enough
During diagnosis, most doctors use the TSH test to evaluate thyroid function and determine the optimal course of treatment. There are times, however, when knowing one’s TSH may be insufficient.
For instance, free T4 in addition to TSH is usually tested if a doctor suspects thyroid dysfunction due to disease of the pituitary gland or hypothalamus.
Likewise, if the TSH is normal, but a person still has symptoms of being hyperthyroid or hypothyroid, free T4 may be checked.
TSH is also not necessarily sufficient to monitor hypothyroidism during pregnancy T4 and free T4 are often recommended.
How Does A Blood Test For Hypothyroidism Work
How to test for hypothyroidism?
Itâs important to note that there is no hypothyroidism test that can check thyroid hormones andâbased only on those test resultsâconclusively determine if someone has hypothyroidism. Thatâs because both thyroid hormone testing and a physicianâs evaluation of symptoms and medical history is required for a diagnosis.
A blood test for hypothyroidism is based on your levels of thyroid-stimulating hormone and the thyroid hormones T3 and T4. Because TSH signals the thyroid gland to produce more thyroid hormones, unusually high levels of TSH can mean that your thyroid isnât making enough hormones.
A thyroid lab test might also measure T3 and T4 to reveal just how low your thyroid hormone levels are, which can help your healthcare provider decide on a treatment strategy.
How Often Should I Get Routine Blood Work
Your doctor will typically recommend that you get routine blood work at least once a year, around the same time as your yearly physical.
But this is the bare minimum. There are several major reasons you may want to get blood tests more often than that:
- Youre experiencing unusual, persistent symptoms. These could include anything from fatigue to abnormal weight gain to new pain.
- You want to optimize your health. Knowing levels of various blood components, such as HDL and LDL cholesterol, can allow you to tweak your diet or fitness plan to minimize unhealthy habits . This can also maximize the nutrients you put in your body and more.
- You want to reduce your risk of disease or complications. Regular blood tests can catch the warning signs of almost any disease early. Many heart, lung, and kidney conditions can be diagnosed using blood tests.
Talk to your doctor first if you want to get certain tests more often than once a year.
Some other tests that you may want include:
- enzyme markers if youre at risk for cancer or other conditions like liver cirrhosis, stroke, or celiac disease
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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.
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
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What Do Thyroid Antibodies Tell You
Three antibodies related to autoimmune thyroid diseases can tell what type of autoimmune disease a person has, and how severe or advanced it might be.
- Anti-thyroglobulin High levels of TgAb are present in 8 in 10 patients with Hashimotos and in 4 in 10 of people being diagnosed with Graves disease.
- Anti-thyroperoxidase High levels of TPOAb are found in 9 in 10 patients with Hashimotos and 8 in 10 of patients with Graves disease.
- Anti-TSH receptor High levels of TRAb are found in 9 in 10 patients with Graves disease and in less than 2 in 10 patients with Hashimotos.
Its important to note that high levels of either TgAb or TPOAb can be found in 1 in 10 of people without an autoimmune thyroid disease, as well as in 2 in 10 of people that are considered healthy.
Theres also a small percentage of people with autoimmune diseases who have no antibodies detected.
TPOAb testing in early pregnancy can predict if a person is at risk of developing postpartum thyroiditis. Postpartum thyroiditis occurs in about 1 in 10 people after giving birth. About 5 in 10 of pregnant people with high TPOAb will develop postpartum thyroiditis .
TgAb or TPOAb are found in 1 in 10 healthy people, more likely females and elderly people .
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 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.
Things That Can Affect Your Thyroid Function Results
Fasting Generally, you dont need to fast before doing a thyroid function test. However, not fasting is sometimes linked to a lower TSH level. This means your results might not pick up on mild hypothyroidism where your TSH levels are only mildly elevated.
Medications Some medications can interfere with your results so its important to tell your doctor about any drugs you take.
Pregnancy Being pregnant can also influence your results. So if youre pregnant make sure to discuss this with your doctor.
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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.
Thyroid And High Blood Sugar
High blood sugar, or hyperglycemia, is a common health concern affecting millions of people. There are two main types of hyperglycemia:
- Fasting hyperglycemia blood sugar levels higher than 130 mg/dl and it usually occurs when a person doesnt eat or drink for more than eight hours
- Postprandial hyperglycemia blood sugar levels higher than 180 mg/dl about two hours after the meal. That being said, nondiabetic individuals rarely have blood sugar levels higher than 140 mg/dl after they eat
The relationship between high blood sugar and thyroid functioning can be discussed from different angles including insulin resistance, metabolic syndrome, and diabetes.
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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.
Why Would I Need These Tests
The thyroid gland‘s hormones help control some of your body’s metabolic processes, such as heart rate, blood pressure, body temperature and weight. Too much or too little of these hormones can make you ill.
You might need thyroid tests if:
- you have symptoms of hyperthyroidism or hypothyroidism
- you are taking some form of thyroid hormone replacement treatment
- you are female and being investigated for infertility
Very rarely, babies are born without a working thyroid gland. For this reason, all Australian newborns are screened for hypothyroidism with a TSH test using a drop of blood taken from a heel prick.
Top 5 Reasons Doctors Fail To Diagnose Hypothyroidism
The Thyroid Federation International estimates there are up to 300 million people worldwide suffering from thyroid dysfunction yet over half are presumed to be unaware of their condition. Hypothyroidism, an underactive thyroid, is one of the most undiagnosed, misdiagnosed, and unrecognized health problems in the world. It is an epidemic that is sweeping the globe yet doctors are failing to recognize and diagnose hypothyroidism. Hypothyroid patients are falling through the cracks of mainstream medicine, left to suffer debilitating and even life-threatening symptoms. What is going on?
Inquire About A T3 Drug
There are many doctors who consider the addition of a T3 hormone, in the form of Cytomel , wholly unnecessary and problematic. They will point to the fact that it is prone to rapid uptake in the intestines and may quickly turn a hypothyroid problem into a hyperthyroid problem. T3 hormones can also interfere with T4 blood test results and complicate the monitoring of your disease. All of these things are true, but to a degree.
If you are able to maintain control of your TSH and T4 but are feeling unwell, the addition of Cytomel may improve your symptoms, according to research from Spain and the National Institute of Diabetes and Digestive and Kidney Diseases.
The same research suggests that the combination of Cytomel and levothyroxine may improve symptoms without any additional side effects compared to levothyroxine alone.
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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.
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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Is There Anything Else I Need To Know About A Tsh Test
Thyroid changes can happen during pregnancy. These changes are usually not significant, but some women can develop thyroid disease during pregnancy. Hyperthyroidism occurs in about one in every 500 pregnancies, while hypothyroidism occurs in approximately one in every 250 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. 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.
Why You May Need A Thyroid Test
Women of all ages are more likely than men to have low thyroid hormone levels. However, many of their symptoms are attributed to other conditions or written off as a consequence of aging.
A blood test for levels of TSH is the most sensitive test for determining whether you have hypothyroidism. Most laboratories use 0.45 5.00 mIU/L as a normal reference range for TSH. People with TSH between 5.00 and 9.99 mIU/L often have no symptoms , but some do. Another test called T4 will be done if your TSH is in this range. A low level of T4 usually means you will benefit from thyroid hormone replacement.
Many people with hypothyroidism or subclinical hypothyroidism aren’t aware anything is wrong because they haven’t been tested. The U.S. Preventive Services Task Force doesn’t recommend thyroid screening because it hasn’t found sufficient evidence that testing thyroid hormone levels in large groups of people without symptoms is cost-effective. Dr. Garber agrees, and suggests a different approachtesting asymptomatic people who are most likely to develop thyroid disease and benefit from treatment.
Treating subclinical hypothyroidism with synthetic thyroid hormone may reduce the risk of developing more serious problems like cardiovascular disease. They note that low thyroid hormone can cause a high cholesterol level and treatment with thyroid hormone may make statin therapy unnecessary.
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