New, sophisticated laboratory tests for measuring low levels of TSH have advanced the role of TSH results in assessing thyroid function. Reseachers from the UK recently published an article in Thyroid Research explaining how the TSH test can be misleading.

Although the article brings up some common points like the question of using a lower TSH range, and there is a focus on hypothyroidism, the main gist is that TSH is not a reliable indicator in many conditions. Treatment for thyroid dysfunction is one example. 

The authors also bring up the question of homeostasis, a topic often ignored by endocrinologists. In hyperthyroidism, a low TSH is a homeostatic mechanism that prevents thyroid hormone levels from rising too high. The references cited in the article are a valuable resource as well for anyone who has had RAI and likely has pituitary antibodies or pituitary dysfunction, that prevents us from having a "normal" pituitary-thyroid-hypothalamic axis. In addition, it's very possible that since we're not producing any hormone of our own, the body may be recognizing that TSH isn't needed.

The researchers, besides explaining how TSH results can be misleading, offer a solution. They propose using an adjusted TSH index based on the FT4 result, a proposal that makes more sense than using the TSH result alone.

Resource:

Rudolf Hoermann and John Midgley. 2012. "TSH Measurement and Its Implications for Personalised Clinical Decision-Making," Journal of Thyroid Research.