TSH or “Thyroid Stimulating Hormone”, the pituitary gland hormone that regulates thyroid function is an extremely sensitive and highly diagnostic test. It is especially valuable in diagnosing developing thyroid hormone imbalances, earlier than any other blood thyroid function test. With this said, it should always be understood that there are some cases when TSH does not accurately reflect the thyroid hormone levels in some patients. This is why, in my opinion, doctors should be ordering more than TSH when diagnosing thyroid diseases but also when monitoring the thyroid hormone replacement therapy, of treated hypothyroid patients.

There are the obvious reasons why TSH is not an accurate reflection of thyroid hormone levels (T-4 and T-3), such as when hypothyroidism is caused by a problem with the pituitary gland itself, which is referred to a “Central Hypothyroidism” (originating from the brain center) or “Secondary Hypothyroidism” (caused by another cause other than the thyroid gland). There are also syndromes referred to as “Low T-3 Syndrome” and “Euthyroid Sick Syndrome”, which are caused by other illnesses that are occurring in the body and result in a low T-3 level, with T-4 and TSH being in normal range. Diseases such as Juvenile Diabetes and a stress related illness called “Wilson’s Temperature Syndrome” can be a cause of low T-3 levels with T-4 and TSH seemingly unaffected. In these cases, a test of the TSH only or even a combination of TSH and T-4, would not detect these low T-3 syndromes.

Other causes however, are not typical and sometimes there is no clear explanation as to why TSH does not accurately reflect the thyroid hormone levels in some patients. I have seen the testimonials of patients who had thyroid hormone levels that were at hypothyroid level but their TSH was in the normal range. When their pituitary function was also tested, to see if that was the problem, test results indicated normal pituitary function. In these cases, there was no explanation for why TSH and the thyroid hormone were not correlating as they should but it is possible that the abnormal pituitary function was sub-clinical (hypopituitarism) and not showing up on the pituitary function tests. It could also be that the patient had other hormone imbalances such as adrenal or sex hormones, affecting the endocrine system as a whole (all glands producing hormones) and causing a problem in communication between the pituitary and thyroid gland.

Giving myself as an example, I have an overall endocrine dysfunction that causes me to need a very, suppressed TSH level, in order for my thyroid hormone therapy for hypothyroidism, to be effective. Unless my TSH is suppressed below normal, my thyroid hormone levels will not reach mid-range or above. While cases like mine are not common, they do exist and I have corresponded with other patients who experience this same scenario. If a doctor started out, testing only my TSH to monitor my thyroid hormone therapy, I would have been under-treated to this day.

I feel with these possibilities, it is only good medical common sense, to test patients diagnostically and in follow up on thyroid hormone therapy, for their levels of TSH, Free T-4 and Free T-3, at least for the first time or two, to make sure the TSH correlates with both thyroid hormone levels.