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Making sense of medicine:Thyroid Blood Tests

Thyroid blood tests are more confusing than most. We are here to help you make sense of them.


The most common thyroid blood test is TSH. This stands for Thyroid Stimulating Hormone, a hormone that is produced in the brain in a gland called the pituitary. It tells us how much your thyroid needs to be stimulated to work effectively. 


If your thyroid is working well, TSH will be in the normal range.

If it is sluggish, the TSH will be higher, as if the brain is yelling at the thyroid to get busy!! This is hypothyroidism.

If TSH is rock-bottom, your thyroid gland is churning out too much hormone and not heeding the regulatory messages from the pituitary. This is hyperthyroidism.

High TSH means low thyroid activity: hypothyroidism

Low TSH means high thyroid activity: hyperthyroidism

Yes, it is counter-intuitive!

Remember, TSH is actually measuring a brain hormone, rather than checking thyroid hormones directly. Western medicine considers the normal range for TSH to be 0.4-4.0. We naturopathic doctors consider the optimal range to be 1-2.


The thyroid makes its own hormones: T4 and T3. These can also be measured by blood tests. Another little confusing factor here is that T3, the activated form of thyroid hormone, has much stronger stimulating effects than T4, so 3 is worth more than 4 in the thyroid bloodwork world! 


T4 is the almost-ready-to-go form of hormone that only needs one simple small chemical reaction to activate it to the more active T3. We like to see both T4 and T3 around mid - normal range.

The main nutrients used in the production of these hormones are L-tyrosine (an amino acid) and iodine. If the thyroid gland is not making enough T4, then these nutrients may need to be supplemented.

The body converts T4 to T3 as needed, primarily in the liver. This conversion requires selenium and zinc. A deficiency of these could affect your ability to convert T4 to active T3: hence your energy and stamina levels may be lower than optimal.

Because TSH, T4 and T3 are so dependent on each other, all three should be tested at the same time for the results to be insightful and meaningful.

It is better to do a thyroid blood test in the morning: those tests catch more cases of low thyroid than tests done in the afternoon. And because levels vary a bit over the day, tests should always be repeated at about the same time of day, for good comparison from one test to the next. If you are on thyroid medications, don’t take them before going in for the test or the hormones from the pills will just have hit your bloodstream as the test is done, giving a falsely high reading.

The TSH test picks up the majority of the worst hypothyroid cases. But optimal thyroid function is so much more subtle than that. There are many ways that the thyroid system can be out of whack, without the TSH necessarily being out range. Because these are less common, they are not screened for with regular bloodwork. As naturopathic doctors we always check these to get the bigger picture.

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