Despite numerous studies showing its lack of sensitivity at diagnosing low thyroid function, TSH continues to be the first (and often only) test used to assess thyroid function in the conventional medical system.
Many of my patients report years of experiencing numerous symptoms of low thyroid function and yet are told that their thyroid function is shown to be completely normal on lab testing. Why would this be so commonplace?
Standard thyroid testing in BC initially involves only a serum (blood) test measuring the amount of thyroid stimulating hormone (TSH) in blood. If TSH is in the normal range, the investigation will not progress any further into testing the actual thyroid hormones (T3 and T4) and antibodies. Those tests are done only if the TSH is deemed to be enough outside of the “normal” reference range. Unfortunately, this sole reliance on TSH to screen for thyroid status is faulty and does not take into account current knowledge of thyroid physiology and evidence based medicine.
TSH alone fails to pick up a significant number of situations where the thyroid is under-functioning. (for more information see below *) A main reason for this is actually quite basic: TSH is produced by the pituitary, a gland in the brain, not the thyroid itself. So what the TSH actually reflects is how the pituitary is doing with respect to thyroid hormones. However, the problem is that most individuals with low thyroid hormone levels in the tissues (the rest of the body) can actually have a very “normal” TSH. In other words for those suffering classic hypothyroid symptoms such as persistent fatigue and unexplained weight gain, their pituitary may well be getting an adequate supply of thyroid hormone even while the rest of the body outside of this gland is not, and so they are usually told they have no “thyroid” problem, end of story, end of investigation.
In naturopathic medicine our training is to dig deeper. NDs are the original functional medicine doctors, interested in how organ systems like the thyroid “function” optimally even before showing up as in frank disease state. We do this using current evidence based medicine research.
In fact there are numerous studies demonstrating that TSH does not accurately reflect T3 (active thyroid hormone) levels in any other body part when the certain conditions are taking place. These conditions include:
- Stress (emotional or physiologic),
- Diabetes and insulin resistance,
- Dieting/calorie restriction,
- Excessive exercise or overtraining
- Weight gain
Many of our patients present with one or several of these conditions while suffering from many classic hypothyroid symptoms and normal TSH and low levels of actual thyroid hormones. And so it is clear that a normal TSH cannot be used as a reliable indicator that a person has normal thyroid at the level of the tissue, only that their pituitary’s needs are sufficiently met. Fortunately, Naturopathic Doctors in BC have access to many other lab tests through Lifelabs and other functional labs in North America that do more thorough and sensitive hormone testing.
What should we use instead?
First step when patients consult with us is to do a thorough history and clinical assessment. If low thyroid function is suspected, we will order a combination of serum (blood) levels of TSH, free T3, free T4, reverse T3 (rT3), antithyroid antibodies (anti- TPO +/or antithryoglobulin antibody). Doctors familiar with the Wilson’s Temperature Syndrome will also use a log of body temperature as an indication of thyroid status and guidance in a specific treatment protocol.
To sum it up, the failure to treat the patients based on a normal TSH without further assessing the thyroid can result in many people with low thyroid function unfortunately being misdiagnosed or mismanaged that would otherwise benefit greatly from treatment.
Croxson MS, Ibbertson HK. Low serum triiodothyronine (T3) and hypothyroidism. Journal of Clinical Endocrinology and Metabolism 1977;44:167-74
Donders SH, Pieters GF, Heevel JG, et al. Disparity of thyrotropin (TSH) and prolactin responses to TSH –releasing hormone in obesity. Journal of Clinical Endocrinology and Metabolism 1985;61 (1):56-9.
Fraser WD, Biggart EM, O’Reilly DJ, et al. Are Biochemical tests of thyroid function of any value in monitoring patients receiving thyroxine replacement? British Medical Journal 1986; 293 (27): 808-10
Koulouri, Olympia et al. Pitfalls in the measurement and interpretation of thyroid function tests. Best Practice & Research Clinical Endocrinology & Metabolism , Volume 27 , Issue 6 , 745 – 762
McDermott MT, Ridgway EC. Sublclinical hypothyroidism is mild thyroid failure and should be treated. Journal of Clinical Endocrinology and Metabolism 2001;86:4585-90.