Many labs only look only at Thyroid Stimulating Hormone (TSH) to assess thyroid health. Unfortunately, this alone offers only a narrow understanding of how your thyroid is working. doesn't give a comprehensive understanding of what’s happening with your health or how to make specific improvements.
We believe it is critical to also measure Free Triiodothyronine (fT3), Free Thyroxine (fT4) and TPO antibodies to fully understand what's happening with your thyroid health and how to make specific improvements. Each test offers a different piece of information that can be used to tailor a treatment plan for your needs.
Thyroid stimulating hormone (TSH) is produced by the pituitary gland in the brain. It's primary job is to regulate the amount of thyroxine (T4) and triiodothyronine (T3) produced by the thyroid. This blood test measures how much overall thyroid stimulating hormone is in your blood. While this is the standard test most doctors authorize, it won’t provide detailed information your thyroid activity. For instance, it may not show problems like your body not being able to use the thyroid hormone that's available.
A normal level of TSH is 0.4 to 5 milli-international units per liter (mIU/L). Levels lower than this may indicate an overactive thyroid, while levels higher than this may indicate an underactive thyroid. Pregnancy and certain medications (like steroids, dopamine, or opioid painkillers) can also cause low levels of TSH.
The thyroid produces two hormones: thyroxine (T4) and triiodothyronine (T3). T4 is mostly inactive. Its primary job as a "storage hormone" is to transport T3 to the proper organs in your body. T4 must be converted to T3 before your body can use it to get energy or deliver oxygen to cells. The T4 test is typically used to determine the level of thyroid hormone in the body; however, because it can be affected by the amount of protein in your blood, it doesn't provide enough information by itself.
Triiodothyronine (T3) is the active version of the thyroid hormone. Thyroxine (T4) must be converted into triiodothyronine (T3) before it becomes usable; this process happens primarily in the liver. T3 circulates the bloodstream both bound and not bound to protein. Only T3 bound to protein can be used by your body.
A total T3 test measures all the T3 in your body, even T3 that’s unusable because it isn’t bound to a protein. This makes the free T3 a crucial test because it only measures the amount of bound T3 in your blood. If you have normal levels of T3, but it isn’t binding well to protein, other thyroid tests won’t indicate that.
Testing for thyroid peroxidase (TPO) measures the levels of TPO antibodies in your blood. If you have high levels of TPO, it may indicate that your immune system is attacking your thyroid hormone as if it’s a foreign invader. This could be caused by an immune disorder like Hashimoto’s disease or Graves’ disease. It's important to include TPO antibodies in a complete thyroid test because you could have high levels of TPO but still show as a normal TSH score.
You can see why a simple TSH test may not be enough to fully understand your thyroid health. If you’re suffering symptoms of a thyroid problem such as fatigue, weight gain, thinning hair, depression, or high cholesterol, you should push for these additional forms of thyroid testing.
Anyone can order an at-home test kit to help understand how your thyroid is working and if there is a need for a further evaluation of your thyroid function.
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