Thyroid Binding Globulin
When thyroid hormones are secreted from your thyroid gland, they are bound to a carrier, a protein. This protein is called “thyroid binding globulin” or TBG. TBG is similar to a taxicab and your thyroid hormones, T4 and T3, get into the cab. They are then transported to the liver (and other areas), where they’re converted into the active “free” form.
Then they jump back into the cab and they’re transported to the rest of the body. You have this little carrier protein / “taxicab” going anywhere and everywhere inside your body. Trouble occurs when there are too many of these carrier proteins. You wouldn’t think this would be a problem, but it is.
Think about TBG like taxicabs at the airport.
If there are a lot of people that need a ride at the airport and limited cabs, the cab drivers will be in a hurry to get the people to their destination and then get back to the airport to pick up more people. If there are a lot of cabs at the airport and only a few people who need rides, the cab drivers are likely to take longer to get the people to their destination because the longer the people are in the cab, the more money they make.
So if there is a lot of TBG, the likelihood of getting active (“free” form) thyroid hormone to the tissues is reduced. It’s as if they all get sucked up by this big sponge.
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 markers done, not just TSH, T3 and T4. You need Free T3, Free T4, T3 Uptake, free thyroxine index, reverse T3, and the thyroid antibodies, in addition to the TSH, T3 and T4.
If your TBG is too high, even though your TSH, Total T4, and Total T3 are normal, your doctor needs to check your T3 Uptake and free hormones to identify this hypothyroid pattern. T3 Uptake and TBG are inversely proportional. So, if T3 Uptake is low, thyroid binding globulin, or TBGs will be high.
Remember that the lab reference range of T3 uptake is extremely broad, where the optimal or functional range is much narrower. So if your doctor does run T3 Uptake, compare it to the optimal or functional range not the lab range.
What causes increased TBG? Excess estrogen elevates TBG.
So where is the excess estrogen coming from?
- Hormone replacement therapy is a common source.
- Birth control pills contain estrogen, so we will often see this pattern in girls and women on birth control medications.
- Some face creams and cosmetics contain undisclosed estrogen.
- Most people don’t recognize that fat cells produce estrogen.
- Any compromise in liver function and detoxification pathways can elevate estrogen levels because the estrogen that should be cleared via the liver is released back into the body. The estrogens can be more potent when recycled. In this situation your symptoms are not caused by a thyroid gland problem, but a problem downstream in the thyroid physiology pathway.
It’s important to realize that there can be many causes of thyroid symptoms. There is more to helping someone with thyroid symptoms than just checking their TSH. We think you are being mismanaged if you have only had your TSH levels tested and were put on medication without asking WHY you have a thyroid problem, WHAT is causing poor thyroid physiology, and figuring out HOW to change the WHY AND WHAT.
This is the reason we like to run full thyroid panels, evaluate blood sugar, red blood cell markers, gut function, liver function, and more. We perform testing other doctors don’t so that we can get to the root cause of what’s happening with the patient.
So to summarize this article; if thyroid binding globulin (TBG) is high, you could have low thyroid symptoms even though you’re taking medications and your TSH and T4 levels are within lab range.
Don’t suffer another minute!
Call Dr. Dranko or Dr. Gorlesky at (919) 556-1033 and schedule your complimentary, no-obligation Meet & Greet today!