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DrChristineM, Veterinarian
Category: Dog Veterinary
Satisfied Customers: 3713
Experience:  6 years in small animal medicine treating dogs and cats.
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What is the difference between T3 and T4 thyroid tests. I know

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What is the difference between T3 and T4 thyroid tests. I know there is more than that(i think six) but it was suggested in one of my other questions that I have my dogs T4 tested instead of T3. I know my vet is going to ask me why I want that test done instead, and I have no idea, other than it was suggested and possibly more acurate.
Hi, I had a glance at the last question to get an idea what has been going with your dog. The T3 test is almost never used in routine testing anymore. Here is what my favorite reference book says about this test (if you want to print and give this to your vet, the book is Clinical Veterinary Advisor, by Etienne Cote)
Tri-Iodothyronine (T3)
Active form of iodine-containing thyroid hormone. Chief function is to increase rate of cell metabolism.
PEARLS: Test is of little diagnostic value. Broad overlap in T3 serum levels within euthyroid, hypothyroid, and euthyroid sick dogs. Total T3 is relatively insensitive and often nonspecific in assessment of hypothyroidism. Total and free T3 provide little additional information over total and free T4 by equilibrium dialysis. Serum T3 correlates poorly with thyroid disease.
The T4, and the free T4 by equilibrium dialysis (ed) are the tests of choice for diagnosis of hypothyroidism.

Does this information help? Let me know if I can answer any other questions...

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Customer: replied 6 years ago.
Thanks so much thats really helpful!
No problem!
Customer: replied 6 years ago.

I just got the results back from my dogs thyroid panel. They said the TT3 was low at 0.7 and the FT3 was low at 1.9. They ran the whole panel, these were the only ones flaged. They are suggesting Thyrolar and or a NAET (holistic) treatment. The three thyroid medications including Thyrolar made him very sick, and months of NAET treatment did nothing. They also suggested Cytomel and said it only deals with the T3's, and I would need to get it from a regular pharmacy. I know you said the T3 wasn't a good test to go on, is the FT3 any better? A year ago the TT3 was 0.5 and FT3 was 3.5 they both have dropped in about a year. He's doing really well right now, playing, eating fine, and seems over all really good. I know sometimes it doesn't matter what it says on paper if he's doing well, but how long can he go with this before it starts causing other problems, and what other problems can I expect out of this( organ damage, neurological?)? Unfortunately my vet seemed very displeased that I did my homework, and wasn't very nice to me. Its like she just wants me to do whatever she says, no questions asked. I can't care for my animals that way, and I really want to understand whats going on with my dog, so I know what to expect.

Can you ask for a copy of the labwork and scan it in here? Did you ask for a FT4? If you asked for a fT4 and they spent your money running a huge thyroid panel...I would have a problem with that. The tests all need to be assessed together to determine what is going on. (I suspect finally the answer is going to be that the bloodwork is showing that he is not hypothyroid, but I would just like to see it myself before I commit to that statement.)

Let me just say one thing: you have a right (and Merl does as well!), to get the proper care but also to be able to ask questions and have them answered. If this vet can't do that, find someone else, someone who will respect your need to know what is going on and who also wishes to do what is best for Merl.
Customer: replied 6 years ago.
Before they did the blood work I specifically asked for the T4 and Free T4. She told me all the t3's and t4's (and some others I don't know much about) are all done when they send it out. Then she tossed the paper at me and said "do you trust me now". When I called today for the results they said the t4 and ft4 was fine just the t3's were low. I can try to get the print out and get it to you in a day or two. We chose this vet because they were traditional and holistic. We were hoping to get a larger range of care and more choices, but I don't think its worth it. We will be seaking out a new vet, I just need to hang in there a bit longer so I can get his medical history without a fuss, and move on.
I guess it may depend on the lab, but I personally have never worked with a lab where you can't either just run a FT4 or a T4 & FT4.
No rush on getting the results, like I said, I think the end result is going to be that there is no cause for alarm. I think finding someone else is a good idea....!
Customer: replied 6 years ago.
Thanks so much, I'll get back to you on the lab work, I'm really interested in what you have to say about it, thanks for your time and care, right now it really means alot.
It's always a pleasure to help someone who cares enough about their furry friend to do the very best for them!!
Customer: replied 6 years ago.

Got the results this morning, I just called so I didn't get the actual paper. These are the results.

TT4 - 31

TT3 - 0.7

FT4 - 23

FT3 - 1.9

T4 - 7

T3 - 3

Thyroid Stimulating Hormone - 12

Thyroglobulin Autoantibody - 5


Let me know what you think.

Unfortunately I need the reference ranges to see where in the range all the values lie (is something high normal, for example or low normal). Every lab has its own set of reference ranges for the tests that they run, so it isn't a universal number or anything I can just look up.
Customer: replied 6 years ago.

oh sorry here it is


TT4 15-67

TT3 1.0-2.5

FT4 6-42

FT3 4.5-12.0

T4 0-20

T3 0-10

Thyroid stimulating hormone 0-37

Thyroglobulin Autoantibody 0-35


hope thats what you were looking for

Yes, that is perfect.

Here's MY interpretation of that data: your dog is NOT hypothyroid and should not be treated for this disease. Unfortunately, we are going to have to look elsewhere for the cause of the skin problems!
Customer: replied 6 years ago.

Atopica or cyclosporine was suggested to me from another vet on this site. I also found a natural product called Mycoplex Coriolus that is another kind of immunosuppressive product. They are all pretty expensive, the last on being the most affordable. It would be nice to deal with the source instead of the symptoms, and it sounded like some of those medications address that. I know all of his issues are stemmed from something, just can't figure out what. We have had so many allergy tests and experimented cutting things out of his diet, but never any clear signs of the cause. Would it be wise to put him on one of these medications? I thought it might address the cause even if we weren't sure what the cause was. He is doing pretty well right now, so I thank you so much for helping us figure out some of the thyroid meds were unnessary. With a dog like this less is more when you are trying to figure out a problem like this.

I think Atopica is an excellent product. I have no experience with Mycoplex Coriolus, so I can't speak for that. I do feel that in general, many of the issues that you discussed in the previous thread are most likely allergy related and it can be very hard to figure out what those allergies are, and even if you do, then what do you do about them? If you can eliminate the allergen (like food), great, do so. But in the majority of cases, the dog is going to have more than just food allergies and so you are left with suppressing symptoms (which is all we do for people, really!). Steroids and Atopica are your best weapons for symptom relief, and of those two, Atopica is less damaging over time. Keep in mind as well, that ideally, with Atopica, you may have to start with twice a day dosing, but the goal is to taper the dog down to the lowest dose (milligram and schedule wise) that keeps symptoms at bay. For example, I may start a large dog at 100 mg once a day until symptoms are gone. Then I may decrease to every other day, then you can try playing with the dose--you can try going to every 3-4 days or dropping the milligrams. Any time symptoms reappear, you have to go back and try again. So at first, it can be pretty expensive, but if it works well, and you can get Merl down to every third day dosing, for example, the cost gets a little better. (And also keep in mind how much you are saving in antibiotics, repeat visits to the vet for hot spots, ear meds, etc, if it works.) The same may be true for the natural product, but like I said I don't have experience with it, so I can't say.
So long story short, yes, I think you should definitely try one of those immune-suppressing drugs and see if it helps.
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Customer: replied 6 years ago.
Thanks so much, I know you have to have a prescription for some of those meds, but we are looking for a new vet who is a little more open minded! I have some direction to go in now and I really appreciate it. Thanks for the education, and your time. I'll probably seek you out in the future, so I'm sure you'll be hearing from me again when we have a plan of action!
Good luck! I would love to hear how this plan works!!