What is a Thyroid Panel?
A thyroid panel is a blood test that measures thyroid hormones within the blood. These hormones are chemical substances that regulate or control the body’s metabolism which helps it function and use energy. Depending on the results of the test, a diagnosis for a thyroid disorder can be made by a professional practitioner.
Why Order a Thyroid Panel?
Your thyroid is a small butterfly-shaped gland that lies at the base of your throat flat against your windpipe. Though it is relatively small, it regulates vital body functions such as body temperature, breathing, heart rate, muscle strength, mood, menstrual cycles and so much more. Your doctor may order a thyroid panel if you exhibit any signs or symptoms of hypothyroidism or hyperthyroidism.
- Muscle weakness, aches, tenderness, or stiffness
- Joint pain, stiffness, or swelling
- Increased sensitivity to cold
- Dry skin
- Thinning hair
- Puffy face
- Weight gain
- Elevated cholesterol levels
- Slowed heart rate
- Menstrual changes (heavy or irregular period)
- Voice hoarseness
- Memory problems
- Muscle weakness
- Enlarged thyroid (goiter)
- Nervousness, anxiety, or irritability
- Tremors in the fingers or hands
- Increased sensitivity to heat
- Thinning skin
- Dry, brittle hair
- Increased appetite
- Sudden weight loss (even with increased appetite)
- Rapid heartbeat, tachycardia (more than 100 beats per minute)
- Irregular heartbeat (arrhythmia) or pounding heart (palpitations)
- Menstrual changes
- Bowel changes (especially more frequent)
- Sleeping difficulty
What Does a Thyroid Panel Measure?
The thyroid panel will measure different thyroid hormones depending on which your doctor orders. The test may be a thyroid antibodies panel, thyroid panel complete, thyroid panel complete with antibodies, thyroid panel with TSH, and thyroid panel with TSH plus Free T3 and Free T4. Prices start from about $49.
The latter is the one that will be described below because these three hormones are the ones that will ultimately determine a diagnosis. If there are strange abnormalities about the results, then one of the others will be ordered thereafter.
Thyroid Stimulating Hormone (TSH)
The Thyroid Stimulating Hormone (TSH) is produced by your pituitary gland which is a tiny organ located behind the sinus cavity below your brain. It stimulates your thyroid gland to release hormones that help control the rate at which your body uses energy. This includes thyroxine (T4) and triiodothyronine (T3) into the blood which will be discussed further down in this section.
TSH is included in the feedback system that your body uses to stabilize thyroid hormones in the blood. It works together with its regulatory hormone called Thyrotropin Releasing Hormone (TRH) which comes from your hypothalamus. When thyroid hormone concentrations decrease, TSH is increased. In turn, TSH stimulates the thyroid gland to produce and release T4 and T3. When your thyroid, pituitary gland, and hypothalamus are functioning normally, your thyroid hormones are relatively stable.
The TSH test determines the level of TSH within your blood. If your doctor suspects you have a hypo- or hyperthyroid condition, he may initially order it alone (outside of a thyroid panel) as a screening test.
Free Thyroxine (Free T4)
Thyroxine (T4) is one of the two major hormones produced by your thyroid to help control the rate at which your body produces energy. In fact, it makes up about 90 percent of thyroid hormones. When your body requires thyroid hormone, your thyroid gland will release it into circulation.
T4 is either bound or not bound to protein. When it is not bound, it is considered “free.” Nearly all T4 in the blood is bound and relatively inactive, but that 0.1 percent that isn’t bound is the free T4 hormone and is biologically active. T4 is converted in the liver and other body tissues into T3.
Both Total T4 and Free T4 tests measure the amount of T4 in your blood and are used to test for or monitor hypo- and hyperthyroidism. In most cases, the Free T4 test is used today as it is not affected by protein levels and thought to be a much more accurate reflection of the T4 thyroid hormone.
Total or Free Triiodothyronine (Total or Free T3)
The other major hormone that works together with T4 in helping control the rate at which your body produces energy is Triiodothyronine (T3). Like T4, it is mostly bound to protein and the free form is biologically active. As a matter of fact, free T3 is four to five times more active than free T4 in circulation.
The amount of free T3 in your blood is measured by the Free T3 test. It is usually used to test for or monitor hyperthyroidism. Like the T4 tests, the Free T3 has replaced the Total T3 because it is thought to be more accurate.
How to Interpret Thyroid Panel Results
Your thyroid tests may be abnormal if the feedback system involving your thyroid gland is not functioning properly. When TSH concentrations are high, your thyroid will try to compensate by making and releasing T4 and T3 in inappropriate amounts.
When your thyroid hormones are low, your metabolism is functioning slowly and your doctor may diagnose you with a thyroid disorder called “hypothyroidism.” If these same hormones are high, your metabolism is high and you’ll probably be diagnosed with “hyperthyroidism.”
- Mild or Subclinical Hypothyroidism: High TSH, Normal T4/T3
- Hypothyroidism: High TSH, Low T4, Low or Normal T3
- Non-thyroidal Illness or Pituitary (Secondary) Hypothyroidism: Low TSH, Low or Normal T4/T3
- Mild or Subclinical Hyperthyroidism: Low TSH, Normal T4/T3
- Hyperthyroidism: Low TSH, High or Normal T4/T3
- Thyroid Hormone Resistance Syndrome: Normal TSH, High T4/T3
What Conditions are Associated with Hypo- and Hyperthyroidism?
The thyroid panel alone is not diagnostic but should prompt your doctor to investigate and perform additional tests to determine the cause of abnormal hormone levels.
The most common cause of thyroid dysfunction is related to autoimmune disease. Hashimoto’s Thyroiditis is a cause for hypothyroidism, and hyperthyroidism may be caused by Graves’ Disease. Hypo- and hyperthyroidism can also be caused by other conditions such as abnormal TSH levels, thyroiditis, or thyroid cancer.
A Thyroid Panel isn’t Always Indicative of Thyroid Disease
A thyroid panel is helpful in determining thyroid dysfunction, and it is helpful to know what tests are involved as well as understand the meaning of the reference ranges of each. However, it doesn’t always predict or reflect thyroid hormone levels. You could have normal or borderline test results and still have a thyroid condition. On the other hand, you may have abnormal levels that are actually caused by pregnancy, estrogen and other drugs, pituitary dysfunction, a systemic illness, or liver disease. Be sure to talk to your practitioner about all your symptoms to help him determine your true condition.