Originally Posted by Void
I hear a lot of similar stories from women with thyroid issues, and it makes me think that "normal range" may have been calibrated based on a male ranges... there has also been some question as to whether the currently established ranges are actually accurate (the ranges are based on a general population average, with the assumption that the median values were asymptomatic/aclinical)
Odds are that the opposite is true, and that thyroid levels (or specifically the optimal TSH levels for maintaining hypothyroid patients) are calibrated for women. Hashimoto's Thyroiditis, the most common cause of hypothyroidism in developed countries, is farmore common in women than men, by a ratio possibly as high as 10-1. There are, of course, other causes of hypothyroidism, such as when patients with thyroid cancer have their thyroid removed.
Part of the problem with thyroid levels is that there are really two optimum ranges for TSH. There's the optimum range in euthyroid (ie healthy) people, where a TSH above a certain level (either 3.0 or 4.5 depending kn who you ask) indicates possible hypothyroidism. However, in patients who have already been diagnosed with hypothyroidism, it may be better to try to keep the patient's TSH levels lower, around 1.0 or possibly even slightly lower.
Partly this is because HT is an autoimmune disease, and so thyroid failure is a gradusl process as the immune system eats away at it, so you want to have some extra space there with TSH levels as thyroid function may continue to drop. Another reason is because as the TSH levels begin to climb, there s a point where they're just not going to increase thyroid function (since the lack of thyroid function is the reason they're climbing in the first place), so by keeping TSH levels lower, what's left of the thyroid can still respond to TSH.
Obviously, an endocrinologist isn't going to want to overshoot and induce thyrotoxicosis (thyroid overdose, basically), especially in older female patients since thyrotoxicosis can wuite literally strip calcium from your bones (not to mention the whole galluping heart rate).
Now, my understanding is that for patients whose thyroid is no longer functional at all, for example if it's been surgically removed, are placed on the full replacement dosage of levothyroxine and the goal is to reduce TSH to 0.005 (ie totally suppressed).
So yeah, part of the problem with treatment decisions based on thyroid tests is making sure to keep a hypothyroid patient's TSH lower than what would ordinarily be an optimal level. Checking FT3 and FT4 levels is useful, but TSH is the main hormone to monitor.