High free but low total values - why??

[milupa]

This is about my dog, but I had similar problems a few hears ago and you were so helpful!

Can you help me and my vet in interpreting very high fT3 and high fT4 with low T3 and T4?

Thybon and L-Thyroxin are being lowered every time tests come back like this, the dosis is now a third from what it was 18 months ago. His kidney, liver, pancreas and digestive system get worse when total T3 and T4 are low.

Antibodies were high when this started in summer 2022.

Otherwise antibodies were not tested since diagnosis of autoimmune hypothyroidism in 2020.

I won’t bore you with blood test results etc, I would really love to get an idea why those numbers can look so out of synch.

Thank you. Everyone have a lovely, stress free third advent weekend.

[greygoose]

There are two types of T4 and two types of T3: bound and unbound. The bound T4/T3 are attacked to protein carriers that transport the thyroid hormones round the body in the blood. But the body can only use that hormone when it is unbound - or, as we call it, Free.

So, the Total T4/T3 tests measure how much total hormone there is in the blood: bound and unbound. The Free tests only measure what is available for use by the body - i.e. free to become attached to a receptor.

What we want to know is how much hormone we have available for the body to use. We're really not interested in the unusable stuff. So, what we should be measuring, and using to dose by, is the Free T4/T3.

If the Free T4/3 levels are high, it would suggest over-medication, which is why the doses are being reduced. But, if he has Hashi's, then it could sometimes be due to Hashi's 'hyper' swings and not the dose. In which case, it's good to keep testing so that the dose can be increased again.

No point in retesting antibodies once you have a positive result, because it doesn't give you any further information. Antibodies fluctuate all the time and there's nothing you can do about them, anyway. They just confirm that the cause of hypo is Autoimmune Thyroiditis, with all that that entails. The antibodies themselves are of no consequence.

[milupa in reply to greygoose]

Oh Greygoose, how lovely of you to answer! How are you?

May I ask: The fT3 is 63, with the range being 3 to 7. BUT the blood sample sat around for 48 hours from blood draw. Could the extreme high value have anything to do with this?

Thank you

[greygoose in reply to milupa]

I'm afraid I can't answer that. But are you sure it was the Free? The results didn't get muddled up, by any chance? Because that is rediculously high. One wouldn't even expect that high with Hashi's. I'd ask for a retest if it were me.

[milupa in reply to greygoose]

Makes sense, I will get that done (in a better lab) early next week.

Again, thank you!

[greygoose in reply to milupa]

You're welcome.