Genetic Testing - Thyroid
Thyroid testing is a complex and certainly somewhat controversial topic.
There are certain things to be aware of when you are testing your animal, or
interpreting the results of a recent thyroid panel. Certainly, concurrent
illness can alter the concentrations of thyroid hormone in the bloodstream, so
you should avoid testing your dog if they have other chronic conditions that you
are aware of, if they are concurrently ill with something acute, if they are
just coming out of a heat cycle or nursing puppies, or if they are on
medications that can interfere with testing.
Some of the most common culprit medications that can decrease T4 or T3 and
falsely elevate TSH include: phenobarbitol (commonly given to animals that
seizure), sulfonamide antibiotics, androgen hormones, phenothiazines (a group of
tranquilizers), propanolol, diazepam, ferosemide (a diuretic), and prednisone.
There are others as well. So, in short, make sure that results are interpreted
either in light of your dog being on these medications, retest after they are
off medications, or talk to your veterinarian to see if you can wait to test
until treatment is complete.
Chronic diseases, especially endocrine disorders, anesthesia, kidney or liver
disease, and heart failure can all affect results as well. Starvation or
chronic weight loss, regardless of cause will also decrease TT4 and T3
concentrations.
Dogs should be at least 6 months old, preferably in the 2-3 year range for 1st
time testing (unless they are showing suspect signs of hypothyroidism already).
The average age of diagnosis is around 7.2 years old, however some breeds like
Golden Retrievers and Dobermans, are being diagnosed at younger ages.
As far as diagnosis itself, one of the most common errors seen in testing is
that sometimes people will only request a TT4 level. This tells you nothing
about that dog's actual thyroid status. It MUST be interpreted in light of
the TSH level as well, or with a concurrent panel like MSU runs with antibody,
etc. While there is still a "gray zone" with many of these
tests, keep in mind that another standard for diagnosis in this case is RESPONSE
TO TREATMENT. In other words, if you dog falls in the "grey zone" and
has minimal clinical signs, you can certainly wait and retest later, or you can
work out a trial supplementation of thyroid hormone with your veterinarian. If
improvement in clinical signs is notes, this is also considered to be diagnostic
for hypothyroidism! Clinical signs for hypothyroidism include (but not
limited to) lethargy, "heat seeking" behavior, mental
"dullness", weight gain, dermatological changes (including dry flaky
skin, "rat tail", or alopecia [hair loss]), hyper pigmentation, poor
wound healing, and/or bruising easily, also repeated infections of the urinary
tract, etc may be a sign of some sort of "immune suppression".
There are many others.
We are currently involved in a study investigating a possible link between
hypothyroidism and urinary incontinence in another large breed of dog. In
the past year, we have seen anecdotal diagnosis of many of these dogs that were
otherwise "unsymptomatic" (i.e. they had none of the above clinical
signs) but were diagnosed based on thyroid panels and response to treatment.
It is certainly very interesting. In some cases with these dogs,
supplementation cleared up other problems these dogs were having, possibly
indicating that thyroid hormone could play a role in many of the body's
functions we haven't thought about yet.
Woops, sorry got off on that tangent. At any rate, one thing to remember is that
one normal thyroid test is not carte blanche to never test again and do as you
please (atleast if you really want to know your dog's total health)--testing
should be done every few years atleast and certainly for dogs that we know are
hypothyroid, to assess whether they are on proper dosage of medications.
It is not and "ignorable" condition, as it may have serious health
consequences.
Hopefully that was helpful, sorry if I rambled.
Lisa Miller
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Doreen Kent ...
A breeder certainly would not take ONE test result as gospel. MSU's
Thyroid Panel has 8 components. The last two - TSH (Thyroid Stimulating
Hormone) & TGAA (Thyroglobulin Auto Antibody) are the signals for genetic
hypothyroidism.
There is an optimum time for testing dogs. A female is best tested 3 - 4
months after she has completed her heat cycle or after she has completed nursing
puppies. Any dog being tested for hypothyroidism should not be tested if
they are stressed in any way - ill, coming off medications or surgery.
If either or both the TSH &/or TGAA results are elevated, it's a red flag.
You should test again 6 months later. If the results are drastically
different, then remains a question. If the results are the same or even
worse than initially reported, then you're dealing with a problem and you can't
bury your head in the sand over it.
Testing for thyroid has become such an emotional issue with breeders. One
breeder recently said to me, "Oh, so what. They have thyroid.
You give them 10 cents worth of pills a day, and they're fine."
Honestly, folks, there are times when I think people share their IQ with someone
else. There are times when I can not argue with such convoluted logic,
because I KNOW my words fall on deaf ears. *Don't confuse me with the
facts - my mind's made up.* It's like trying to convince the guy who
called the house not long ago not to breed his unpapered, pet, rescue female.
"Oh, she has such a wonderful personality." Yeah, sure, so do
blind dates.
Thyroid test your dogs. Do it often. Do it on all your dogs.
Watch for patterns in test results. You can't tell a puppy buyer that
their puppy has no known genetic defects if you don't look for them. If
you're a puppy buyer, ask if the sire and dam have been tested free of
hypothyroidism by a recognized thyroid testing lab - not Bob's lab around the
corner from the vet's office.
I'm not advocating looking for trouble. I'm advocating rooting it out.
Doreen Kent