Most people are under the misunderstanding that Thyroid Stimulating Hormone (TSH) test properly tests thyroid function.   However, when you examine this hormone, it is not a good measurement to evaluate the overall function of the thyroid. People mainly decide to do this test because they are struggling with fatigue, gaining weight, losing weight, or struggling with other hormonal issues.

According to the American Thyroid Association , “A high TSH level indicates that the thyroid gland is failing because of a problem that is directly affecting the thyroid (primary hypothyroidism). The opposite situation, in which the TSH level is low, usually indicates that the person has an overactive thyroid that is producing too much thyroid hormone (hyperthyroidism).”

There are several reason why TSH should only be a part of the equation for evaluating thyroid. Thyroid hormones regulate the speed at which your cells work.  This controls your metabolism because the faster your cells work, the more energy you will need via food. The hypothalamus generates Thyroid Releasing Hormone (TRH) that signals the pituitary to tell the thyroid gland to produce more TSH. TSH is a hormone released by the pituitary gland that tells the body to make more thyroid hormones.  The thyroid makes about 80% thyroxine (T4) and about 20% triiodothyronine (T3). T3 is the active thyroid hormone and T4 must be transformed into T3 mainly in the liver by removing an iodine atom from the molecule. T3 helps regulate this rhythm, but that is dependent on T4 levels being turned into T3 levels.  Stress and inflammation cause the biggest imbalance in transforming T4 to T3.

As you can see, TSH is only one part of the equation for thyroid function, in addition, TSH is regulated based on two elements

1) TSH has a diurnal rhythm.  TSH levels reach a maximum level between 2:00- 4:00 AM and a low between 4:00- 8:00 PM.

Depending on the time of day, TSH levels might be higher, lower, or normal based on the rhythm of the body.  Unless time of day is taken into consideration, TSH might be “off” for a reason.

2)TSH is like a thermostat.  When T4 levels are high, TSH will turn off because the body does not need to generate more thyroid hormone.  When T4 levels are low, the body will increase TSH because they body needs to produce more thyroid hormone.

TSH tells us one thing only, how much thyroid hormone our body THINKS that we need to be making.  People might still be having thyroid issues, but have TSH levels that are in range.  We must do further testing to explore what is going on at the cellular level.  I recommend having a thyroid panel or TSH, Free T3, Reverse T3, Free T4, TPO, Ferritin, and Vitamin D.

Contact our office for more information.

Health and Happiness (^_^)


American Thyroid Assocaition. “Thyroid Function Tests.” American Thyroid Assocaition. 2016.

Issacs, Scott. MD, FACP, FACE. “Hormonal Balance, 3rd Ed.” Colorado. 2012.

  1. Russell, R. F. Harrison, N. Smith, K. Darzy, S. Shalet, A. P. Weetman, and R. J. Ross. “Free Triiodothyronine Has a Distinct Circadian Rhythm That Is Delayed but Parallels Thyrotropin Levels” Journal of Clinical Endocrinology Metabolism 93: 2300 –2306, 2008.

Thyroid Function Tests