What are thyroid function tests?
Thyroid function tests are a series of blood tests that measure how well your thyroid works. Available tests include TSH, T4, T3, T3RU.
The thyroid gland is a small gland located in the lower front part of your neck. It is responsible for the regulation of many of the body's processes like mood, energy generation and metabolism.
The thyroid gland produces two major hormones: thyroxine (T4) and triiodothyronine (T3). If your thyroid does not produce enough of these hormones, symptoms like depression, lack of energy and weight gain may occur. This condition is called hypothyroidism.
If on the other hand your thyroid produces too many hormones, symptoms like anxiety, mania, tremors and weight loss may occur. This is called hyperthyroidism.
In general, a doctor who is worried about your thyroid hormone levels will order broad screening tests, such as: T4 or the TSH test (Thyroid Stimulating Hormone). If these results are abnormal, your doctor will order further tests to determine the cause of the problem.
Blood collection for thyroid function tests
Tell your doctor if you are pregnant or take medicine. Certain medications and pregnancies can affect your test results.
A blood draw (venipuncture), is performed in a laboratory or a doctor's office. When you arrive to take the test, you are asked to lie down on a cot or stretcher or to sit in a comfortable chair. If you wear long sleeves, you will be asked to roll up a sleeve or take your arm off your sleeve.
A nurse or a technician will tie a rubber band tightly around your upper arm to allow the veins to swell with blood. As soon as the technician finds a suitable vein, he will insert a needle under the skin and into the vein. When the needle pierces your skin, you may feel a sharp prick. The technician will collect your blood in test tubes and sends it to a laboratory for analysis.
When the technician collects the amount of blood he needs for the tests, he will pull the needle out and apply pressure to the puncture wound until the bleeding stops. The technician will then put a small bandage over the wound.
You are free to continue with your normal daily activities immediately.
Side effects and aftercare
A blood sample is a routine, minimally invasive procedure. The days following after the blood draw, you may experience pain or mild bruising at the site where the needle was inserted. An over-the-counter painkiller or an ice pack can relieve your discomfort.
If you are in severe pain or the area around the puncture is swollen and red, contact your doctor immediately. These can be signs of infection.
Understanding your test results
T4 and TSH results
T4 test and TSH test are the most common thyroid function tests. In most cases, they’re ordered together.
The T4 test is also known as the thyroxine test. A high T4 level indicates an overactive thyroid (hyperthyroidism). Symptoms are diarrhea, unplanned weight loss, anxiety and tremors. Most of the T4 in your body is bound to protein. A small part of T4 isn’t and this is called free T4. Free T4 is the form that is available to your body. Sometimes a free T4 level is also tested along with the T4 test.
The TSH test measures the level of thyroid hormone in your blood. The TSH has a normal test range between 0.4 and 4.0 milli-international hormone units per liter of blood (mlU / L).
If you show signs of hypothyroidism and have a TSH above 2.0 mIU / L, you may be at risk of developing hypothyroidism. Symptoms are depression, weight gain, fatigue and brittle hair and fingernails. Your doctor will probably want to perform thyroid function tests at least every two years in the future. Your doctor may also decide to treat you with medications such as levothyroxine to relieve your symptoms.
Both the T4 and TSH tests are routinely performed in neonates to identify a malfunctioning thyroid gland. Developmental disabilities may occur if this condition called congenital hypothyroidism is left untreated.
T3 test checks the levels of the hormone triiodothyronine. It is often ordered when T4 tests and TSH tests indicate hyperthyroidism. The T3 test can also be ordered if you show signs of overactive thyroid and your T4 and TSH levels are not elevated.
The normal range for T3 is between 100 and 200 nanograms of hormone per deciliter of blood (ng / dL). Higher levels than normal most commonly indicate a condition called Graves' disease. This is an autoimmune disease associated with hyperthyroidism.
Results of T3 resin uptake
The binding capacity of a hormone called thyroxine-binding globulin (TBG) is measured by a T3 resin uptake (T3RU) blood test. Your TBG binding capacity should be low, if your T3 level is elevated.
Abnormally low levels of TBG often indicate that the body doesn’t get enough protein or a problem with the kidneys. Abnormally high TBG levels indicate a high level of estrogen in the body. High levels of estrogen can be caused by obesity, eating foods rich in estrogen, pregnancy or hormone replacement therapy.
Your doctor may order an ultrasound test or a thyroid intake test if your blood work suggests that your thyroid is inactive or overactive. These tests examine structural problems with the thyroid gland and activity and any tumors that may be causing problems. Based on these findings, your doctor may want to remove tissue from the thyroid gland to look for cancer.
Your doctor may prescribe medication to regulate your thyroid activity if the scan is normal. Just to make sure the medication works, they will perform additional thyroid function tests.
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