The thyroid gland is located at the front of the neck and consists of two lobes, one on each side of the windpipe and adjoined by a small strip of thyroid tissue known as the isthmus. Thyroid problems can be identified by measuring the level of free T3 (FT3) in the blood. High levels indicate an overactive thyroid whereas low levels indicate an underactive thyroid.
The three hormones produced by the thyroid are:
- T3 (triiodothyronine)
- T4 (tetraiodothyronine)
- Calcitonin
T3 and T4 are the active forms of the thyroid hormone, thyroxine, and are involved in the regulation of:
- The body’s metabolic rate
- Heart function
- Digestive function
- Muscle control
- Brain development
- Bone maintenance
TSH is the most sensitive biomarker for thyroid function and is often used to ensure the hormone replacement therapy you are prescribed is working as effectively as it should.
High levels of T3 and T4 often indicate an overactive thyroid, whereas low levels indicate an underactive thyroid.
What is a Normal Range for a Thyroid Test?
Laboratories use reference ranges when analyzing the function of the thyroid. Typical reference ranges for a healthy individual may look like this:
- TSH 0.27– 4.2 mIU/L
- FT4 12.0 – 22.0 pmol/L
- FT3 3.1 – 6.8 pmol/L
Different laboratories use different reference ranges, but if your results fall outside of these parameters you could be diagnosed with hypothyroidism or hyperthyroidism.
Symptoms of hypothyroidism
• Feeling tired or having little energy
• feeling cold
• gaining weight
• Dry skin
• Depression
• Constipation
Symptoms of hyperthyroidism
• feeling hot or sweating
• Fast heart rate
• Weight loss
• Diarrhea
• Muscle weakness
• Fertility concerns
How Often One Should Get Thyroid Levels Tested?
Thyroid tests can identify hypothyroidism or hyperthyroidism. How often you repeat these tests depends on your diagnosis, however, you will need a TSH test once a year if you have hypothyroidism, and more regular tests if you have hyperthyroidism to identify that the treatment is working.
The frequency of testing will be determined by your GP upon diagnosis of your condition.