TSH is not a thyroid health indicator

TSH (thyroid stimulating hormone) is a hormone released by the pituitary gland that basically instructs the thyroid gland on how many thyroid hormones to produce.

• If the thyroid hormone levels in the blood is too low, then the TSH increases so that the thyroid gland makes more thyroid hormones.
• If the thyroid hormone levels in the blood is too high, then the TSH decreases so that the thyroid gland makes less thyroid hormones. 

So looking that TSH, that should give you a good idea what is happening with your thyroid, right?  Unfortunately not.

Problem 1: TSH is not enough

The first challenge is that TSH is a hormone produced by the brain in response to the level of thyroid hormones in the blood.  So while TSH is the gold standard for thyroid hormone level testing, it doesn’t measure the actual level of hormones in the blood.  Furthermore, it does NOT give any indication of how these thyroid hormones are actually used by the body (or not used).  

To give an extreme example: you could have adequate levels of thyroid hormones in your blood, and so your TSH is “normal”.  But your body is not using the thyroid hormones as it should (for various reasons), and you may experience debilitating hypothyroid symptoms.  Despite a “normal” TSH.

Problem 2: The reference ranges for what is considered “normal” for TSH has been criticised for being too broad

Reference ranges are important measured created by the lab to determine if the result of the test is normal or abnormal. 

The first challenge is that the assumption that these lab reference ranges are generated from the test results of healthy, disease-free people.  Therefore, we can use these reference ranges to evaluate if your TSH is normal or not. 

Unfortunately, that is an incorrect assumption. Lab reference ranges are created from the population of people who have their labs tested – therefore, people who are not in optimal health (because why then would they have their blood tested? Healthy people don’t get blood work done).

The second challenge is that the doctors use a reference range of TSH to be “normal” if it is between 0.5 to 4.2 mIU/L [1].  This was established by the NHANES III (National Health and Nutrition Examination Survey). But the upper limit of TSH is an ongoing debate and labs have different upper limits.  

To make matters more complicated, is that the AACE (American Association of Clinical Endocrinologists) guidelines for doctors stated that an elevated TSH, usually above 10 mIU/L (with a low level of T4) is an indication of hypothyroidism [1].  So, the doctor may not consider treating your for hypothyroidism until your TSH is above 10.  Even if you experience hypothyroid symptoms.  

Functional medicine doctors use a much narrower reference range for TSH, more in range of 1,8 to 3 mIU/L.  

Problem 3: When TSH is suppressed or too low

There are circumstances when the TSH can be pushed too low (called a suppressed TSH) by certain medications and supplements.  When this happens, your doctor may think that you are over-treated with thyroid hormone replacement therapy, and reduce your medication – even though you are not over-medicated or show signs of hyperthyroidism (overactive thyroid). 

Let’s have a look at a few scenarios:

• Biotin, a well-known supplement in the vitamin B family, is known to interfere with thyroid lab results, especially TSH.
• If you take T3 medication (in addition to your T4 medication), it may suppress your TSH lab result.
• If you are on T3-only treatment, the TSH result is even less informative, and can be volatile in results (for reasons that is not for this newsletter). 

My thoughts: if your doctor is only evaluating your thyroid’s function based on TSH and T4,it is time to reconsider your doctor.  Fire your doctor, and find a doctor who is willing to do the blood tests needed, and who knows how to interpret it.