There are, however, many pitfalls with relying too heavily on TSH alone.

The Pitfalls of Focusing on TSH

Although TSH is the gold standard of thyroid testing, there are several known pitfalls with using TSH as a measure of overall thyroid function.

• TSH levels vary diurnally by up to 50% of mean values; it peaks around midnight and drops to it’s lowest around noon. So, depending on when you test your TSH, your values may change [6]
• Recent experiments showed there could be variation of 40% when measuring at the same time of day for multiple days in a row [7]
• These 40-50% changes to TSH do not reflect change to the actual thyroid function
• National academy of clinical biochemists have indicated that 95% of individuals without evidence of thyroid disease have TSH below 2.5 mIU/L. Recommendations have been made to lower the upper limit to 2.5 mIU/L.

TSH Affects More than the Thyroid

It’s widely known that TSH has receptors on the thyroid, hence the direct impact on thyroid hormones.

However, TSH receptors also exist on many other tissues throughout the body, such as the brain, testes, kidneys, heart, bone, thymus, lymphocytes, adipose tissue and fibroblasts [5]. Since TSH isn’t only having an impact on the thyroid, we really shouldn’t be so surprised when TSH and thyroid hormones don’t match the relationship we expect. Sometimes a patient will have high TSH and normal thyroid hormones or low TSH and normal thyroid hormones. When this is seen in the clinic, it’s easy to focus on the thyroid, but doctors and patients need to realize TSH may be indicating issues outside of the thyroid gland.

Various Factors Impact TSH

Stress and Trauma

Stress suppresses TSH. Stress can result from examinations (tests) [8]

Infection

Infections will alter T3, carrier proteins and increase TSH. Thyroid function typically decreases during times of infection [9].

Aging

It’s widely accepted that TSH and free T4 and T3 change with age [10].

Medications and Drugs

Various drugs can affect TSH secretion, including: Dopamine agonists, Glucocorticoids, Somatostatin analogues, Rexinoids, Metformin, Amphetamine, and caffeine  [2]

Chronically Sick or Critically Ill

This refers to people suffering from Low T3 Syndrome or euthyroid sick syndrome. These conditions are considered non-thyroidal illnesses, which represent altered thyroid hormones in critically ill patients. They may have elevated or lowered TSH [15].

Summary

TSH is usually a good indicator of thyroid function. In some cases, TSH does not accurately reflect thyroid symptoms. It’s important to realize TSH is associated with processes other than thyroid function, and various factors can affect TSH.

At Absolute Health and Wellness, we consider more in-depth lab testing when TSH doesn’t accurately reflect thyroid function.