Thyroxine-binding globulin

[ctizzle13498]

---

Members don't see this ad.

Whats the big deal about this? Is it the same concept as Sex Hormone Binding Protein, where that the amount of free testosterone is whats important, and that if its bound to this, then it is "inactive."

I think I have a note from DIT saying that during Pregancy, increase TBG levels, but free T4 is normal. Wouldn't T4 decrease if TBG increased?

 

[1badvette]

Whats the big deal about this? Is it the same concept as Sex Hormone Binding Protein, where that the amount of free testosterone is whats important, and that if its bound to this, then it is "inactive."

I think I have a note from DIT saying that during Pregancy, increase TBG levels, but free T4 is normal. Wouldn't T4 decrease if TBG increased?

due to increase in estorgen during pregnancy , the live increases synthesis of all binding proteins , so TBG will increase , but T4 will stay normal due to increase in T4 production by the thyroid ..

 

[ctizzle13498]

So wait, why is the thyroid making more T4?

 

[Phlame217]

Okay:

Liver increases TBG, so more TBG in blood.

Extra TBG binds T4 and so thyroid replaces free T4 to get levels back to normal.

Result:

If you do labs on a pregnant woman, her Total thyroid will be elevated but her free thyroid will be normal. This is relevant because if you're ever working up a pregnant woman, its a normal variant to have elevated total thyroid levels. BUT before you rule out hyperthyroidism, you must order free thyroid levels.

 

[ctizzle13498]

Thank you! That makes PERFECT sense 🙂

 

[theTruth_97]

so what happens in the scenario where a person is taking steroids or has liver failure and their TBG has decreased.....does total thyroxine levels decrease but free T4 remain the same aka normal?

 

[theTruth_97]

bumping up for immediate help! Please!!

 

[FlashTime_91]

so what happens in the scenario where a person is taking steroids or has liver failure and their TBG has decreased.....does total thyroxine levels decrease but free T4 remain the same aka normal?

Hmmm that's a good question. I was actually wondering the same thing a few weeks ago when doing the endocrine section. Could someone please explain this?

 

[Qester]

I have a question adding to this line of thought.

From my understanding Steroid use and nephrotic syndrome decrease TBG. However Hepatitis increases TBG. Can anyone explain to me why hepatitis would result in an increased TBG?

 

[scoKraz4]

I have a question adding to this line of thought.

From my understanding Steroid use and nephrotic syndrome decrease TBG. However Hepatitis increases TBG. Can anyone explain to me why hepatitis would result in an increased TBG?

Acute hepatitis will probably have increases TBC b/c it is secreted as an acute phase protein in reaction to the inflammation related cytokines. In chronic hepatitis it would probably be decreased due to long-term destruction and improper functioning hepatocytes.