Earlier this month, one of my blogs focused on thyroid function testing. The main point I wanted to make was that ‘normal’ thyroid function tests do not necessarily mean all is well with the thyroid and health. The blog focused on research that shows that even with the ‘normal’ range, higher levels of the hormone known as thyroid stimulating hormone (raised levels of which generally mean low thyroid function) are associated with increased body weight.
This week saw the publication of a study in a similar vein . In this case, the researchers involved in this study were looking at the relationship between TSH (also known as thyrotropin) levels and risk of death due to a heart-related condition (heart attack being the main cause here).
Again, this study focused on TSH levels in the ‘normal’ range, which the researchers cite as 0.5-3.5 mlU/L. This is interesting in itself, as the lab I usually use for these tests quotes and upper limit of TSH of 4.20, and I saw a patient yesterday who came with some blood test results where the upper limit of TSH was quoted as 5.50! it seems there is a lack of consensus about what the normal range of TSH should be�
Anyway, focusing back on the study, the research looked at the risk of cardiac death in a group of about 17,000 women and 8000 men over a period of something more than 8 years.
They found no significant relationship between TSH levels and cardiac death risk in men. However, in women, it was a different story. Compared to women with a TSH level of 0.5-1.4 (relatively low levels which should mean relatively high thyroid function):
Women with a TSH level of between 1.5-2.4 were found to be at a 41 per cent increased risk of cardiac death.
Women with a TSH level of between 2.5-3.5 were found to be at a 69 per cent increased risk of cardiac death.
Here again, it seems a study has found that ‘normal’ but perhaps somewhat impaired thyroid function is associated with negative consequences for health.
Managing thyroid issues can be tricky, but I do think there is a case for treating some people with ‘normal’ biochemistry if their clinical picture suggests low thyroid function. Biochemical testing can be important, but at least as important, in my humble opinion, is to make treatment decisions on what a doctor sees and hears in front of him or her.
Quite a few doctors I know express concern at the thought of someone with ‘normal’ test results taking thyroid hormone. They often cite the risk of treatment, including risks to the heart. Obviously, I think it’s a good thing that as doctors we should be aware of the risks associated with thyroid hormone treatment. I just wish more doctors would see the other side: that there can be considerable risks associated with not treating too.
1. Asvold BO, et al. Thyrotropin Levels and Risk of Fatal Coronary Heart Disease: The HUNT Study. Arch Intern Med. 2008;168(8):855-860