If you or your doctor suspect that you have a thyroid imbalance, the standard course of action is to run a TSH test. TSH stands for “thyroid stimulating hormone” and it’s made in the pituitary gland. Yes, that’s right, TSH is not made by the thyroid, it’s made by a gland in the brain. Now you might be wondering- why are we looking at a hormone made in the brain to assess the thyroid? That’s a great question!
TSH is an indirect way to look at your thyroid. I like to describe TSH as a doorbell. It’s a signal from the brain (ding-dong!) to the thyroid to make thyroid hormones (T4 and T3- which we’ll talk about in a minute). The assumption is that when your thyroid hormone levels drop, TSH will rise to stimulate the thyroid. The problem is that a TSH test on its own doesn’t tell us much. Is the thyroid responding properly to TSH and making T4 and T3?
T4 is the main hormone produced by the thyroid gland so it is a much more direct way to see how your actual thyroid is doing. If T4 levels are low, it means your thyroid is sluggish and isn’t making enough thyroid hormone. Keep in mind that T4 is a weak and mostly inactive hormone. Its main goal is to be converted into T3 which is the active thyroid hormone which gives you energy, helps you maintain a healthy weight, balances your mood and regulates body temperature. In my opinion, T3 is the MOST IMPORTANT thyroid hormone to test because it’s the one that is actually doing all the work and helping you feel good. TSH is just a signal. It has no direct impact on your weight, energy or mood.
Low T3 levels are incredible common and I can’t tell you how many women I see in my practice who have a low T3 hormone but their TSH is perfectly normal. So, if your doctor is only checking your TSH levels, they could tell you that everything looks great when in reality you may have low T4 and T3 hormone levels causing symptoms of hypothyroidism.
For a full picture of how your thyroid is working, I recommend getting a full thyroid panel that includes the following tests:
- Free T4
- Free T3
- TPO (thyroid peroxidase) antibodies
- TG (thyroglobulin) antibodies
- Reverse T3
To learn more about each of these tests and the optimal ranges to look for, check out my 5 Essential Thyroid Tests for Women.