Well, it's deja vu all over again. Pan went in for her annual physical on
Monday, and while we were at it, we did a geriatric panel (she's only 5 1/2,
but in a breed with short lifespan, I suppose that's getting old). The test
results just came back, and while everything else looked good, her T4 levels
came back low. On a scale where 1 - 5 is normal, she's a 0.5. The vet is
of the opinion that since she's most definitely not borderline, we go ahead
and start supplementing and do a full panel in 2 or 3 weeks.

This seems reasonable to me. Would anyone have any idea just how likely it
is that the T4 levels are not at all indicative of actual Thyroid function?
Near as I can tell, there have been no behavioral/physical changes in her
ever since we've had her - her energy levels are fine (although she excels
at holding the couch down), her skin/coat condition are fine, she's nowhere
near being fat, etc.

Thankfully, the symptoms of Hyperthyroidism is quite blaringly obvious.
I'll at least know if the pendulum swings in that direction.

Suja

"Suja" wrote in message
news:GrhQg.64$XX2.9@dukeread04...
her T4 levels
came back low. On a scale where 1 - 5 is normal, she's a 0.5. The vet is
of the opinion that since she's most definitely not borderline, we go
ahead
and start supplementing and do a full panel in 2 or 3 weeks.

This seems reasonable to me. Would anyone have any idea just how likely
it
is that the T4 levels are not at all indicative of actual Thyroid
function?

........ Both T3 and T4 can be altered by non-thyroidal illnesses. Was the
T4 the only test run? RIA T4 just isn't that accurate. Thyroid meds may
perk her up, but that doesn't mean she has thyroid problems. Give a normal
dog thyroid meds and they'll seem more active. I disagree with your vet,
even though I think that hypothyroidism is often under diagnosed. I'd go
for the full panel now if you really want to know if it's a thyroid problem.
This could also be test error, in which case you'd be treating a
non-existent disease. The other scenario is that there's something else
going on that is not being addressed by assuming the test result is a
reflection of thyroid function. I think to run a thyroid test the dog has
to be off thyroid meds, but don't remember for sure. Something you'd need
to check on.

Thankfully, the symptoms of Hyperthyroidism is quite blaringly obvious.
I'll at least know if the pendulum swings in that direction.

.........I doubt if a small dose of thyroid meds will cause symptoms of
hyperthyroidism.

buglady
take out the dog before replying

"buglady" wrote in message:

....... Both T3 and T4 can be altered by non-thyroidal illnesses.

You know, I keep reading that. But no one has mentioned what those
illnesses might be. I did ask if it is possible that something else could
be causing the T4 to be suppressed, and she said that given the other
bloodwork (on the receipt, it says Super Chem/CBC/T4), she didn't think so.

Was the
T4 the only test run? RIA T4 just isn't that accurate.

It was part of the geriatric panel, so yes, T4 was the only test run as part
of that. The vet basically said that in her experience, she hasn't met any
dogs that test this low not be hypothyroid, and it's not worthwhile testing
for something she can almost guarantee is a problem, and then again in two
or three weeks.

Suja

"Suja" wrote in message
news:dKwQg.125$XX2.38@dukeread04...
.. But no one has mentioned what those
illnesses might be.

http://siriusdog.com/articles/thyroi...dogs-t3-t4.htm
*The protein-bound portion of TT4 can be lowered by non-thyroid illnesses,
other hormones (cortisol) and certain drugs. Drugs that can lower
protein-bound T4 (and therefore TT4) include steroids (cortisone,
prednisolone, prednisone, etc.), non-steroidal anti-inflammatory drugs
(phenylbutazone and others), anticonvulsant or seizure drugs
(phenobarbital), certain potentiated sulfa drug antibiotics and potentially
other drugs. Therefore, a dog with normal thyroid gland function could have
a low TT4 due to lowering the protein-bound portion of TT4.*

.........So any illness that lowers blood protein will also lower TT4. Since
the value can also be affected by hormones, I would think that high cortisol
(Cushings and/or stress) might affect the value.

Also if the dog is sick with something else (anything else) then the thyroid
decreases output as a self-protective mechanism for the body (euthyroid is
normal thyroid):
http://www.ngrc.org.uk/default.asp?a...inary%20Advice
*The most important factor that needs consideration, is the effect of
non-thyroidal illness. During times of illness and stress, thyroid hormone
concentrations often decrease (low T4 (or T3) state of medical illness
previously known as "euthyroid sick"). This is considered to be an adaptive
protective mechanism that, by lowering metabolic rate, helps preserve
resources to increase the chance of recovery. Physiologically, it would seem
unwise to override this adaptation with exogenous thyroid hormone. In human
medicine, there is no clear indication that such supplementation is
beneficial and some evidence to suggest that exogenous thyroid therapy could
negatively influence recovery from certain non-thyroidal
illnesses...........................The administration of certain
pharmaceutical preparations can also reduce plasma thyroid hormone
concentration. Classic examples are barbiturates and glucocorticoids. The
effect of barbiturates is further complicated by the duration of therapy but
it is thought that central effects, altered protein binding and hormone
metabolism/clearance have a role in these drug effects. TSH concentrations
generally do not increase during drug therapy and it is likely that this is
another example of an adaptive process that reduces thyroid hormone
concentrations appropriately and in the long-term interests of the animal.

However the "sulpha" group of antimicrobials given for long enough at
sufficient doses can actually cause a reversible primary hypothyroidism
including both decreased thyroid hormones and increased TSH.

Other factors that can influence thyroid hormone concentrations include
exercise, diet and the reproductive cycle. However, during the normal course
of events these influences are not of sufficient magnitude to compromise
diagnostic interpretation with regard to the presence or absence of
hypothyroidism.*

I did ask if it is possible that something else could
be causing the T4 to be suppressed, and she said that given the other
bloodwork (on the receipt, it says Super Chem/CBC/T4), she didn't think
so.
.........you don't have a copy of bloodwork?

The vet basically said that in her experience, she hasn't met any
dogs that test this low not be hypothyroid, and it's not worthwhile
testing
for something she can almost guarantee is a problem,

........Up to you. Is this the first T4 you've ever had run? And how many
times did the vet actually get a 6 panel test done when the TT4 showed low
from a regular test so the results were verified?

http://www.diamondsintheruff.com/healthandbehavior.html
Research done at Auburn University indicates that in-house T4 tests are
unreliable and inaccurate 52% of the time in dogs. "Having treated lots of
animals for hypothyroidism, the most important thing I can recommend is the
[full] panel versus the total T4. Every time I think that you can tell
something by doing a total T4, I'm mistaken," says Dr. Whitney Pressler,
DVM. -Whole Dog Journal article, "Help for Hypothyroidism", June 2005

http://www.ngrc.org.uk/default.asp?a...inary%20Advice
*The mainstay of thyroid diagnosis for dogs in general is the combination of
serum T4 and TSH with FT4d and TgAA for additional suport (Graham and Mooney
2005). Total T3 is not currently favoured.

Total T4 (TT4) is relatively inexpensive and easily available. It has good
diagnostic sensitivity, in that few cases of hypothyroidism are missed by
TT4 measurement. An exception is when hypothyroid dogs have T4
cross-reacting species of TgAA (T4AA) in their circulation which cases false
normal or false high T4 values to be generated by most assay systems.
Unfortunately, mostly for the non-thyroidal reasons mentioned above, TT4 has
very poor diagnostic specificity with many subnormal T4 values being due to
things that are not hypothyroidism. Diagnostic specificity has been reported
as low as 75% for TT4 (Dixon and Mooney 1999), meaning that of dogs that
present with signs similar to hypothyroidism but that do not have the
disease, 25% will have subnormal T4 concentration (due to physiological
response to non-thyroidal illness) and a false positive diagnosis.

TSH would be expected to elevated in cases of primary thyroid failure, but
unfortunately, it is not a perfect test for hypothyroidism either. TSH
measurement does have better diagnostic specificity than TT4, i.e., few
non-thyroidal conditions cause a high TSH value. However, disappointingly,
not all hypothyroid dogs have the expected high TSH. The proportion that do
not has been variably reported but compared to gold-standard TSH response
testing the figure probably lies between 15 and 20% (Dixon and Mooney 1999).

It makes sense that the combination of TT4 and TSH has the potential to
benefit from the advantages of each (good sensitivity of TT4 and good
specificity of TSH). Indeed, at prevalence levels of 10%, the positive
predictive value (PPV) of T4/TSH ratio exceeds 80% when TT4 alone would have
a PPV of less than 30%.

That means that if a positive result is obtained from a T4/TSH ratio, the
clinician could be more than 80% confident that the patient was truly
hypothyroid. In contrast, faced with a positive (subnormal) TT4 result alone
less than 30% of such cases will actually have the disease. At the same time
negative predictive value (NPV) of the T4/TSH ratio is excellent at around
99% meaning that almost complete confidence can be had that a dog with a
normal T4/TSH ratio does not have hypothyroidism.........................In
the general canine population, the laboratory diagnosis of hypothyroidism is
less than perfect but the combination of a minimum of T4 and TSH greatly
improves the chance of a correct diagnosis over the use of TT4 alone. The
addition of FT4d can help when the presence of non-thyroidal concurrent
illness, drug therapy or T4AA is suspected or known.*

..........Just curious, did your pup have a rabies vaccine recently, or any
vaccine?
http://www.dvmnewsmagazine.com/dvm/a...l.jsp?id=35188

Although this study claims it refutes Purdue's 6 yr study:
http://www.jvetintmed.org/perlserv/?...0.1892%2F0891-
6640(2006)20%5B818%3ALOABRV%5D2.0.CO%3B2

buglady
take out the dog before replying

"buglady" wrote in message:

........you don't have a copy of bloodwork?

No, because she called to give me the results yesterday. I already had
Thyroid meds for Khan, so we're just using those for her as well, and I
haven't gone back, so don't have a copy of the bloodwork.

Is this the first T4 you've ever had run?

On her, yes.

And how many
times did the vet actually get a 6 panel test done when the TT4 showed low
from a regular test so the results were verified?

Don't know. Her credentials are pretty good, and she's worked at Cornell,
so I took it at face value. I am guessing that she's of the opinion that
this is a true result because she's not on any medication that could've led
to the low values and her other test results don't support this being the
result of something else. I'll call tomorrow and talk to her - she was not
in today and tomorrow is her surgery day; hopefully she'll have a little
time for a chat.

.........Just curious, did your pup have a rabies vaccine recently, or any
vaccine?
http://www.dvmnewsmagazine.com/dvm/a...l.jsp?id=35188

She had her Rabies vaccine the same time as the blood draw. We're on a once
every three year protocol for Rabies, and she's titered for Distemper/Parvo
in lieu of boosters.

Thank you for all the information, Buglady. I will bring this up with the
vet. I am uncomfortable with medicating a dog who doesn't really have any
symptoms, and we'll see if the serum lipid/cholesterol has been measured and
backs up the theory. Hopefully, they have enough leftover blood to do a
full Thyroid panel if it comes to that.

Suja

"Suja" wrote in message
news:QMGQg.160$XX2.155@dukeread04...
Is this the first T4 you've ever had run?

On her, yes.

And how many
times did the vet actually get a 6 panel test done when the TT4 showed
low
from a regular test so the results were verified?

Don't know. Her credentials are pretty good, and she's worked at Cornell,
so I took it at face value. I am guessing that she's of the opinion that
this is a true result because she's not on any medication that could've led
to the low values and her other test results don't support this being the
result of something else

.......I'm not saying she's absolutely wrong, but if she doesn't really know
if a 6 panel backs up her diagnosis made on just one TT4 with no symptoms,
well, I don't know, it makes me uneasy. I think my first response would
have been, I wonder if this is an error. My second response would have been
well, we can wait and redo or get a full panel. That greyhound site had a
funny bit about humans with thyroid problems not liking to back down the
thyroid meds to normal levels because they liked being slightly thyrotoxic!
Even on a normal (euthyroid) person/dog, thyroid meds will give you a boost,
sort of like drinking coffee all day! So just getting a response from the
meds WRT something like activity level, isn't really proof the dog was
hypothyroid, unless they had a lot of symptoms that got resolved. And
there's still always the issue of a batch gone wrong at the lab. This isn't
out of the realm of possibility.

I am uncomfortable with medicating a dog who doesn't really have any
symptoms, and we'll see if the serum lipid/cholesterol has been measured
and
backs up the theory.

............Luckily, hypothyroidism isn't any kind of emergency, which means
you can wait and see a bit, especially since your dog has zero symptoms.
Just because you have one hypoT dog doesn't mean you'll have another, unless
they're related. Now if you had a batch of cats and the problem was HyperT,
well, that's a whole 'nothr bag as you can get a whole colony of cats with
the same thyroid issues.

Hopefully, they have enough leftover blood to do a
full Thyroid panel if it comes to that.

........I don't know where they sent your bloodwork, but I wouldn't bother
sending blood for a full thyroid to anywhere else but Michigan State. There
are other approved places - the OFA site has a list. The full test isn't
exactly cheap, so I just wouldn't trust anyone but the most well known to do
it. Plus your stats go in a database they're amassing on incidence of hypoT
in breeds - a worthwhile project.

buglady
take out the dog before replying