What Is Thyroid Function Testing?

A number of blood tests may be used to learn if your thyroid gland is working normally. These function tests reveal if your thyroid is producing the right amount of thyroid hormones. Thyroid blood tests may be ordered:

  • To check for thyroid disease before it causes symptoms, especially in newborns
  • To diagnose an underactive or overactive thyroid
  • To determine if an underlying disorder, such as Hashimoto’s thyroiditis, Graves’ disease, thyrotoxicosis, or thyroid inflammation, may be causing an underactive or overactive thyroid
  • To evaluate a lump on the thyroid gland, called a thyroid nodule
  • To evaluate an enlargement of the thyroid gland, called a goiter
  • To monitor treatment for thyroid disorders

Understanding how your thyroid is functioning enables your doctor to treat a thyroid disorder if one is present.

The Role of Thyroid Function Tests

Thyroid function testing can be used in several ways, including:

  • Diagnosis – this testing aims to find the cause of symptoms. Thyroid function testing can reveal whether the thyroid gland is functioning normally or abnormally and what specific disorder you may have.
  • Screening – this is testing for disease in the absence of symptoms. All newborns in the U.S. are routinely screened for an underactive thyroid. Some adults may also be screened for thyroid disorders, although not all experts agree that this is beneficial.
  • Monitoring – thyroid blood tests provide valuable information about whether treatment for thyroid disorders is working as it should or if it needs adjustment.

Who should get testing?

Thyroid function testing is often ordered when patients have symptoms of a thyroid disorder. Testing can assist with diagnosing or ruling out thyroid problems as a cause of your symptoms.

Many of the symptoms of common thyroid problems are nonspecific; there is a wide range of diseases and disorders which may cause them. Thyroid function testing, which may be referred to as a full thyroid panel, complete thyroid panel, extended thyroid panel or other thyroid lab tests, may be included with other tests to evaluate if you are having trouble with a non-specific symptom like fatigue, depression, or difficulty becoming or staying pregnant.

In addition to being used for diagnosis, thyroid function tests may be performed to screen for thyroid disease in patients who have no symptoms. Newborn infants are routinely screened for hypothyroidism shortly after birth.

Screening for thyroid disease in adults is controversial. Some experts recommend screening certain groups who are at higher risk of having an underactive thyroid. These risk factors may include:

  • Age
  • Family history of thyroid disease
  • Personal history of type I diabetes
  • Personal history of autoimmune disease
  • Personal history of radiation to the head and neck

Other experts do not recommend routine screening for thyroid disorders in adults. The U.S. Preventive Services Task Force, which issues screening recommendations, has concluded that there is currently not enough evidence to assess the benefits and drawbacks of screening for thyroid disorders.

Thyroid function tests are also used for treatment monitoring. Patients with known thyroid disorders will have periodic thyroid function testing to ensure their treatment is effective.

Best Overall Thyroid Function Test
Labcorp Standard Thyroid Test

Price: $89
Type: In-person collection
Sample: Blood
Tests for: TSH, free T4
Results timeline: 1 business day

The Labcorp Standard Thyroid Test is conducted at your nearest Labcorp facility and requires a simple finger prick for sample collection. This test measures two key metrics:

  • Thyroid-stimulating hormone: TSH for short, this hormone produced in the pituitary gland regulates production of the T3 and T4 hormones. Since it’s a sensitive marker, TSH is often used to screen for thyroid diseases and conditions.
  • Free T4: In addition to T3, T4 is the other main thyroid hormone. Fluctuating T4 levels are strong indicators of an overactive or underactive thyroid gland.

After your lab visit, you should receive results within one business day of your sample being analyzed.

Types of Thyroid Function Tests

A number of blood tests may be used to screen for and diagnose thyroid disorders. Below are some thyroid function tests that may be used for screening and diagnosis:

Thyroid test

Thyroid-Stimulating Hormone (TSH) Test

T4 test

T4 Test

T3 test

T3 Test

More Thyroid Function Tests

Getting Thyroid Function Testing

Thyroid function tests are typically ordered by a primary care physician, endocrinologist, or another medical professional. These tests are most often performed in a doctor’s office, clinic, medical lab, hospital, or another medical setting.

Costs of thyroid testing

The cost of a thyroid test will vary by location and test type. Some clinics, usually community or nonprofit clinics, offer free or low-cost testing. Labs, clinics, and at-home testing companies may accept insurance to cover or lower your cost of testing. If you order you own thyroid lab tests, that could impact the cost of testing as well. As for how much blood work for thyroid costs without insurance, that depends on your testing facility.

Types of sample collection

A blood sample is required for a thyroid panel test. If you’re giving a sample in a lab, expect a blood draw. At home, you’ll fill in blood spots.

Getting test results

Typically, your doctor will interpret several thyroid function test results along with your symptoms and health history to determine whether a thyroid disorder is present.

It often takes a few business days before the results of your thyroid function test(s) are available. You may receive the results by mail or through an online health portal, or your doctor may schedule an appointment to review the results with you and discuss the next steps.

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