When thyroid hormones are secreted from your thyroid gland, they are bound to a carrier, a protein. This protein is called “thyroxine-binding globulin” or TBG. So TBG is similar to a taxicab, and your thyroid hormones, T4 and T3, get into the cab, and they are transported to the liver, where they’re converted. And then they jump back into the cab and they’re transported to the rest of the body. You have this little carrier going anywhere and everywhere inside your body. Trouble occurs when there are so many of these carrier proteins called TBG, these little taxicabs, that the normal free amount of T4 and T3 that should be floating around isn’t. It’s as if they all get sucked up by this big sponge, by all these little taxicabs, these thyroid-binding globulins.
Here’s the thing…your TSH will look normal, your total T4 will look normal, your total T3 will look normal. If those are the only markers your doctor is checking, then the problem is completely missed. This is why you need ALL of the thyroid testing done, just not TSH, T3 and T4. You need TSH, Resin T3 Uptake, free thyroxine index, reverse T3, and the thyroid antibodies, in addition to the TBG thyroxine-binding globulin, Free T3, Free T4, and Total T4. If your TBG is too high, even though your TSH is normal, including T4 and total T3, your doctor needs to check your T3 Uptake. It will show that, actually, the T3 Uptake is low when the thyroid binding globulin, or TBGs are high.
Remember that the lab reference range of T3 uptake is extremely broad, where the optimal or functional range is much narrower. Excess estrogen elevates TBG also. Birth control pills contain estrogens. Some face creams and cosmetics contain undisclosed estrogens. And these estrogens can elevate in your body and they’re detoxified through the liver. If you have poor liver function, or inability to detoxify, this is yet another reason you could still have thyroid-type symptoms. It’s not necessarily a thyroid gland problem, but it’s more of a liver problem.
It’s important to realize that there can be many more causes of thyroid malfunction! More than just, “My TSH is low.” Again, we want to do all the testing and get to the root cause of what’s happening with the patient. If thyroxine-binding globulin (TBG) is high, you could have low thyroid symptoms, but normal lab numbers, even though you’re taking medications.
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