The only accurate way to check your thyroid is through a blood test.
Thyroid Function Test
A thyroid function test is performed to determine if there's a problem with your thyroid. This test measures the levels of specific hormones in your blood.
Hormones Measured
The primary hormones measured in a thyroid function test are:
- Thyroid-Stimulating Hormone (TSH): This hormone stimulates the thyroid gland to produce thyroid hormones.
- Thyroxine (T4): This is the main hormone produced by the thyroid gland. Doctors may refer to the "free" form of T4, known as FT4.
How the Blood Test Works
- A blood sample is taken from a vein in your arm.
- The sample is sent to a laboratory for analysis.
- The lab measures the levels of TSH and T4 in the blood.
- A doctor interprets the results to determine if your thyroid is functioning properly.
Example of Interpreting Results
| Hormone | Normal Range (Example) | Possible Interpretation |
|---|---|---|
| TSH | 0.4 - 4.0 mIU/L | High TSH: Possible hypothyroidism |
| Low TSH: Possible hyperthyroidism | ||
| FT4 | 0.8 - 1.8 ng/dL | Low FT4: Possible hypothyroidism |
| High FT4: Possible hyperthyroidism |
Note: Normal ranges can vary slightly depending on the laboratory.
Why You Might Need a Thyroid Function Test
You might need a thyroid function test if you are experiencing symptoms of:
- Hypothyroidism (underactive thyroid)
- Fatigue
- Weight gain
- Constipation
- Dry skin
- Hyperthyroidism (overactive thyroid)
- Weight loss
- Anxiety
- Rapid heartbeat
- Sweating
