Table of ContentsView AllTable of ContentsPurposeTest TypesWhat to ExpectSide EffectsInterpreting Results
Table of ContentsView All
View All
Table of Contents
Purpose
Test Types
What to Expect
Side Effects
Interpreting Results
Thyroid blood tests are an important part of diagnosing and treating thyroid disease. Based on how high or low the different values are—including key hormones such as TSH and T4—the lab can determine which type ofthyroid diseaseyou have (hypothyroidism vs. hyperthyroidism) and narrow the possible causes.
The results can be difficult to understand because the diagnosis can change based on the relationship of values. For instance, a high TSH and low T4 may suggest Hashimoto’s disease, while a low TSH and high T4 may suggest Graves' disease. Different combinations of values can mean different things, and there is often more than one meaning.
1:24How to Work With Your Thyroid Medical Team
1:24
How to Work With Your Thyroid Medical Team
Why You May Need a Thyroid Test
Thyroid tests are done to determine how well thethyroid glandis working. This gland, situated in the front of your throat, produces hormones that regulate heart rate, blood pressure, digestion, metabolism, and other body functions.
When you have thyroid disease, your thyroid gland produces too little or too much of a hormone. The tests will help diagnose the type of disease, which can fall into two broad categories:
If you have a family history of thyroid disease or symptoms of an imbalance of thyroid hormones, your doctor may order these tests. With hypothyroidism, symptoms include weight gain, fatigue, and a slow heart rate.With hyperthyroidism, the overproduction of hormones can cause weight loss, agitation, and a racing heart.
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Types of Thyroid Function Tests
Thyroid-Stimulating Hormone (TSH)
When thyroid hormone levels are low, more TSH is produced to stimulate production. When levels are normal, the pituitary gland stops producing TSH.
The TSH test measures how much or how little TSH there is in the bloodstream.
Thyroxine (T4)
There are two types of T4: bound T4 (which is attached to proteins that prevent it from entering tissues) and free T4 (which is not attached to proteins and can enter tissues freely).
When measuring T4, the lab will look at two different values:
Free T4 is arguably more important to measure because it is the type that will be more active once converted to T3.
Triiodothyronine (T3)
Triiodothyronine(T3) is the active thyroid hormone converted from T4. As with T4, there is both bound and free T3.
T3 blood tests include:
Is T3 or T4 More Important?T4 is generally the more important thyroid hormone to measure. This is because it describes how much thyroid hormone is available for use rather than how much has been converted.
Is T3 or T4 More Important?
T4 is generally the more important thyroid hormone to measure. This is because it describes how much thyroid hormone is available for use rather than how much has been converted.
Thyroglobulin (Tg)
Thyroidectomy(surgical removal of the thyroid gland) or radioactive ablation (RAI) therapy are commonly used to treat thyroid cancer. A high Tg level is a sign that cancer cells are still present after these treatments.
By comparing baseline values with later values, the Tg test can tell your provider if cancer treatments are working. It can also tell them if the cancer is inremission.
Thyroid Antibodies
Some thyroid diseases like Hashimoto’s thyroiditis and Graves' disease areautoimmune disorders. These are diseases in which the immune system targets and attacks normal thyroid cells.
There are three common antibodies associated with autoimmune thyroid disease:
Thyroid Binding Proteins
These blood tests measure the amount of proteins that can bind to T3 and T4. They can help determine the cause of a thyroid problem if your thyroid gland is functioning normally.
The tests include:
What to Expect During the Test
Thyroid blood tests involve a basic blood draw, also known as a venipuncture. You will be seated while a skilled nurse orphlebotomistperforms the procedure, which takes a few short minutes to complete.
You may feel a pinch when the needle is inserted or withdrawn and there may be some bruising after the procedure.
Side Effects of Thyroid Tests
While there is little risk of complications with a thyroid blood test, it does involve a blood draw that may cause side effects such as:
In rare instances, a skin infection may occur. See a healthcare provider immediately if you develop a fever with chills; a pus-like discharge; and increased swelling, redness, pain, or heat at the puncture site.
What Results Mean
The results of thyroid blood tests are described in a reference range of values. The reference range has a high and low value between which results are considered normal. Values near the upper or lower limit are borderline, while anything outside of these limits is considered abnormal.
Normal thyroid levels for adults are as follows:
Thyroid disease may also besubclinical, meaning that there is only mild thyroid failure, usually with few notable symptoms.
Reference ranges and units can vary from lab to lab. To ensure consistency in your test results, use the same lab for every test.
Thyroid Disease Healthcare Provider Discussion GuideGet our printable guide for your next healthcare provider’s appointment to help you ask the right questions.Download PDFEmail AddressSign UpThank you, {{form.email}}, for signing up.There was an error. Please try again.
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TSH Interpretations
On its own, the TSH test can diagnose thyroid disease, albeit with limitations.
According to the American Association of Clinical Endocrinologists (AACE) and the American Thyroid Association (ATA), TSH values can be interpreted as follows:
Comparing High/Low TSH and T3/T4 Levels
While the TSH test is valuable, it is more useful when referenced to T3/T4 results. By comparing TSH with T3/T4 values, your healthcare provider may have a clearer picture of the cause of thyroid disease.
TSHT3/T4InterpretationsLowHighPrimary hyperthyroidism, most often due to Graves' diseaseHighLowPrimary hypothyroidism, most often due to Hashimoto’s thyroiditisLowNormalSubclinical hyperthyroidismHighNormalSubclinical hypothyroidismNormal to lowLowCentral hypothyroidismNormal to highHighMay be caused when a person becomes resistant to hypothyroid treatment or has a TSH-producing pituitary adenomaOther InterpretationsOther thyroid tests may be included in the workup. Some have specific aims, while others are used for screening purposes or to evidence possible causes.RT3 testscan detect euthyroid sick syndrome (ESS), a condition in which abnormal thyroid hormone levels are due to an illness unrelated to the thyroid gland.Tgtestscan be used to predict long-term treatment outcomes. Research has shown that 4% of people with aTg level under 1will experience cancer recurrence within five years.TPOAb testscan help confirm Hashimoto’s disease if TSH is high and T4 is low.TRAb testscan helpdiagnose Graves' disease or confirm a diagnosis oftoxic multinodular goiter.SummaryMany thyroid blood tests are available, including tests for the thyroid hormones T3 and T4, thyroid stimulating hormone (TSH), and thyroid antibodies. The combined results can paint a clearer picture of the cause of thyroid disease. The tests can also monitor how effective thyroid treatments are, including the treatment of thyroid cancer.
Other Interpretations
Other thyroid tests may be included in the workup. Some have specific aims, while others are used for screening purposes or to evidence possible causes.
Summary
Many thyroid blood tests are available, including tests for the thyroid hormones T3 and T4, thyroid stimulating hormone (TSH), and thyroid antibodies. The combined results can paint a clearer picture of the cause of thyroid disease. The tests can also monitor how effective thyroid treatments are, including the treatment of thyroid cancer.
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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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