There are several types of tests to check how well your thyroid gland is working. Your doctor may order one or more tests to determine a diagnosis, plan your treatment, or monitor your condition overtime. Here are some common tests used to assess thyroid health.
Thyroid Function Tests
Thyroid function tests are the most commonly ordered tests to investigate thyroid hormone disorders.1 A sample of your blood will be collected in a tube and sent to the laboratory.2
A thyroid function test tells you if your thyroid gland is working properly by measuring:
- Thyroid stimulating hormone (TSH)
TSH controls the amount of thyroid hormones produced and released by the thyroid gland. It is secreted by a small structure in the brain called the pituitary.1
- Thyroxine (T4)
T4 is the main thyroid hormone produced by the thyroid gland and accounts for 85‒90% of the thyroid hormones in the thyroid gland.1
- Tri-iodothyronine (T3)
T3 is produced in smaller amounts (about 10‒15%) by the thyroid gland. T4 is converted into T3 in various tissues when needed by the body.1
Both TSH and T4 are commonly ordered together as a panel test:
- High TSH and low T4 levels indicate that the thyroid gland is not making enough thyroid hormone due to an underactive thyroid gland (hypothyroidism)2
- Low TSH and high T4 levels indicate that the thyroid gland is making too much thyroid hormone due to an overactive thyroid gland (hyperthyroidism)2
Thyroid autoantibody tests
An abnormal thyroid function test will prompt your doctor to order additional blood tests to determine the underlying problem. In patients with autoimmune thyroid diseases, such as Graves’ disease and Hashimoto’s thyroiditis, the body’s immune system produces antibodies that reacts against thyroid cell proteins. Measuring the level of thyroid antibodies will help diagnosed the type of autoimmune disorder affecting the thyroid gland.3
Thyroid uptake scan
The purpose of this scan is to determine if the thyroid nodule is producing too much thyroid hormones in a patient who have concomitant hyperthyroidism. During this procedure, a small injection of a radioisotope (known as the tracer) is given. A thyroid nodule which takes up more of the tracer than normal thyroid tissue does is known as a” hot” nodule. “Hot” nodules are rarely cancerous. In some cases, the nodule takes up less of the tracer than normal thyroid tissue. This nodule is known as a “cold nodule”. It is not possible to distinguish between a cold nodule which is cancerous and one that is not. This will depend on presence of suspicious imaging features on thyroid ultrasound (often performed together with the thyroid uptake scan) and possible further evaluation by fine needle aspiration biopsy.
Ultrasound scan
An ultrasound scan is a procedure that uses high-frequency sound waves to generate pictures of the thyroid gland. Doctors use it to examine the size, shape and changes of a thyroid nodule. They are helpful for monitoring thyroid nodules that are not surgically removed, to see if they grow or shrink over time.7
Fine-needle aspiration biopsy
Your doctor may perform a thyroid biopsy if a suspicious nodule is detected on the ultrasound scan.2 This is a procedure (usually performed by a specialist) whereby a small needle is introduced into the thyroid nodule under ultrasound guidance to obtain cells for further analysis in the laboratory to determine if the nodule is cancerous (malignant) or non-cancerous (benign). Usually, a few samples from the same nodule will be taken in the same setting to increase its accuracy. The procedure is generally of minimal risk and the patient usually can return to work or home after the biopsy.
Summary
- The thyroid function test is the most commonly ordered test to investigate thyroid hormone disorders.
- An abnormal thyroid function test will prompt your doctor to order additional blood tests, imaging and/or biopsy procedures to determine the underlying problem.
