Interpreting Thyroid Function Test Results
While normal ranges may vary from lab to lab, generally each hormone should fall within a reference range that is considered normal. Acceptable ranges are:
TSH: 0.4-4.5 mIU/mL
Tg Ab: < 1.0 IU/mL
Some institutions may use narrower ranges depending on how the blood is analyzed in the lab. When looking at your results, typically there is a reference range listed so you know if the measurement is normal for that specific lab.
If your results are outside the normal range, this may indicate temporary fluctuations in thyroid function rather than a longer-term thyroid condition. And day-to-day variation in levels can be normal and part of a healthy, responsive endocrine system.
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.
What Is The Thyroid Gland
The thyroid gland is a butterfly-shaped endocrine gland that is normally located in the lower front of the neck. The thyroids job is to make thyroid hormones, which are secreted into the blood and then carried to every tissue in the body. Thyroid hormones help the body use energy, stay warm and keep the brain, heart, muscles, and other organs working as they should.
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How Do Tsh Values Change With Age
- 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 .
Thyroid Function With Antibodies Blood Test
This tests for thyroid-stimulating hormone , free thyroxine , free triiodothyronine and thyroid antibodies.
If you have a family history of thyroid or autoimmune disease, you are more likely to develop one yourself. With this test, you can tell if your thyroid hormones are functioning within the healthy range. You can also detect any abnormalities caused by an autoimmune disease. Even if your thyroid function is currently normal, elevated antibodies may increase your risk of developing a thyroid disorder in the future.
Why this test?
The Thyroid Function with Antibodies Blood Test is for you if you suspect that you have a thyroid condition. Or, you have a family history of thyroid or autoimmune disease and want to check if you have elevated antibodies.
This test is also for people taking thyroid medication and who want to monitor their thyroid hormones and antibodies.
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Will I Need To Do Anything To Prepare For The Test
In most cases, you don’t need any special preparations for a thyroxine blood test. Certain medicines and supplements may affect your test results, so let your provider know what you’re taking, but don’t stop any medicines without talking with your provider.
If your provider has ordered more tests on your blood sample, you may need to fast for several hours before the test. Your health care provider will let you know if there are any special instructions to follow.
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 test is 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 provider 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 provider 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 providers office should reach out to you within a matter of days to walk you through the results of your thyroid test.
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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.
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 Is It Used For
A TSH test is used to find out how well your thyroid is working. It can tell if you have hyperthyroidism or hypothyroidism in your blood. But a TSH test can’t show what is causing a thyroid problem.
If you take prescription thyroid hormone medicine because of hypothyroidism or because you had your thyroid removed, you’ll have regular TSH tests to check your thyroid hormone levels. TSH tests are also used to monitor your thyroid hormone levels after treatment for hyperthyroidism.
Blood Tests For Your Thyroid
Blood tests are the easiest and fastest way for doctors to assess your hormonal balance and health.
Thyroid function tests are one of the most common lab tests most of the time they will clearly show if your thyroid is underactive.
However, sometimes the test results can be confusing. How can the same normal range fit almost any person of any age, gender, and physical state?
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When Is A Thyroid Function Test Done
A thyroid function test is requested in a variety of situations, including if you:
- have signs or symptoms of an underactive thyroid gland or an overactive thyroid gland
- have signs of problems with your pituitary gland
- are taking medicines that can affect your thyroid function, such as amiodarone and lithium
- are a woman with infertility problems
- are taking thyroid medicine, such as thyroxine, to monitor how you are responding to it.
Sexually Transmitted Infection Tests
Many sexually transmitted infections can be diagnosed using a blood sample. These tests are often combined with urine samples or swabs of infected tissue for more accurate diagnoses.
The following STIs can be diagnosed with blood tests:
Blood tests arent always accurate right after contracting an infection. For an HIV infection, for example, you may need to wait at least a month before a blood test can detect the virus.
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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.
How To Test For Thyroid Problems At Home
How to check your thyroid hormones at home?
The Everlywell at-home thyroid test can tell you if your thyroid hormone levels suggest hypothyroidism. This thyroid function test requires only a few drops of blood as a sample. After getting your online test results, you can easily see your levels of thyroid-stimulating hormone , free T3 and T4, and TPO antibodies. High TSH and/or low T3 and T4 can indicate hypothyroidism.
You can also take our thyroid test at home to check your hormones for indications of hyperthyroidism. Hyperthyroidism means your thyroid gland is overactive: itâs producing too many hormones. Low levels of TSH and/or high T3 and T4 can suggest hyperthyroidism.
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Undetected Low Levels Of Thyroid Hormone May Underlie Subtle Changes That Can Increase Your Risk Of Cardiovascular Disease
For a gland only two inches in size, the thyroid has a huge influence on our health. It produces a hormone that is carried in the bloodstream to all parts of the body. Thyroid hormone plays a major role in regulating metabolismthe process by which body cells convert nutrients into energyand thereby helps regulate body temperature, heart rate, and even brain function. So when thyroid hormone levels fall, the body slows.
You’re probably aware of the common symptoms of low thyroid hormonefatigue, fuzzy-headedness, weight gain, cold hands, and dry skin. But if you’re like most of us, you’re likely to blame your diet and exercise regimen instead of your thyroid if your cholesterol levels and weight are creeping up, especially if you don’t have any of the other symptoms of low thyroid. “Symptoms are often nonspecific, and since women over 60 generally have more of these nonspecific symptoms, their doctors may not think to test for hypothyroidism,” says endocrinologist Dr. Jeffrey Garber, associate professor of medicine at Harvard Medical School and author of The Harvard Medical School Guide to Overcoming Thyroid Problems.
How Does The Thyroid Gland Function
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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When Is It Ordered
A thyroid panel may be ordered when you have signs and symptoms that suggest underactive thyroid or overactive thyroid due to a thyroid disorder.
Signs and symptoms of an underactive thyroid may include:
- Trouble tolerating heat
- Sometimes more frequent bowel movements
- Some uncommon problems that can affect the eyes: puffiness around the eyes, dryness, irritation, excessive tearing, light sensitivity, blurry double vision
- In some cases, bulging of the eyes
- Less frequent or lighter menstrual periods in women
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.
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Is Tsh Over 25 Indicative Of Disease
1 in 10 of people with TSH values above 3.0 mIU/L has Hashimotos .
TSH itself, as a marker of disease is not enough. If you have any symptoms connected to thyroid, talk to your health provider and get the full thyroid blood work done. This is the best first step towards understanding the health of your thyroid.
Thyroid Disease In Pregnancy
Currently, there is insufficient evidence to advocate for universal screening . Based on the 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum, if a woman is pregnant or planning pregnancy, TSH testing is indicated if she has any of the risk factors listed in Table 314. Pregnant women often experience symptoms that can be non-specific or vague and as such, it may be difficult to distinguish between symptoms of thyroid dysfunction and normal changes of pregnancy. Clinicians should have a low threshold for TSH testing in pregnancy.
Table 3. Risk Factors for Thyroid Disease in Women who are Pregnant or Anticipating Becoming Pregnant14
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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 .