Why Are My Dog's TSH Results Abnormal ?
Why Are My Cat's TSH Results Abnormal ?
To see what normal blood and urine values are for your pet, go here
For an explanation of causes of most abnormal blood and urine tests go here
To see how tests are often grouped, go here
Ron Hines DVM PhD
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Your Pet's Thyroid Stimulating Hormone Assay
This is another test your veterinarian might order when he or she is uncertain if your dog or cat has thyroid gland problems.
Perhaps your pet’s T-4 results were a borderline number or perhaps it was only slightly high or low and your veterinarian is still uncertain if a true thyroid problem exists. You see, your pet’s T3 and T4 levels can be low due to many non-thyroid health issues.
The TSH test is part of a group of tests that examine your pet’s thyroid gland function in detail. They are called a thyroid panel. If the costs of lots of lab tests are a concern, having your vet simply run a free T4 and TSH are a good way to begin.
TSH (thyrotropin) is produced in your dog or cat’s pituitary gland, a tiny bleb on the bottom of its brain that produces an amazing array of hormones that regulate its entire body.
The area just above your pet’s pituitary gland (its hypothalamus) is constantly measuring the amount of thyroid hormones (T3 & T4) in your pet’s circulation. When those levels drop too low, more TSH is released to stimulate its thyroid gland to produce more T4. So high TSH levels suggest that not enough thyroid hormone is present. A low level of TSH suggests that enough, or more than enough, thyroid hormone is being produced. However the TSH test in dogs and cats is not as accurate in sorting out thyroid gland problems as it is in humans. The reasons why remain unclear.
A TSH assay is included as part of the OFA screening of potential breeding dogs for any genetic tendency toward hypothyroidism. So far, setters, spaniels and Shetland sheepdogs have the highest tendency toward that defect.
Reasons Why Your Pet’s TSH Levels Might Be High :
In dogs, high TSH levels are suggestive of hypothyroidism, but normal or low TSH results do not necessarily rule it out. About 70% of true hypothyroid dogs will have high TSH levels. But even quite elevated TSH levels are occasionally found in dogs that have no symptoms of hypothyroidism. We do not know why, but those high TSH levels should not be used to diagnose hypothyroidism unless your pet’s free T4 levels are low as well and other non-thyroid illnesses have been eliminated as the possible cause.
Dogs with non-thyroid illnesses sometimes have high TSH levels as well.
Cats that have had successful radioactive iodine treatment for hyperthyroidism requiring thyroid supplement can be expected to have high TSH levels thereafter.
Reasons Why Your Pet’s TSH Levels Might Be Low :
Hyperthyroid cats will generally have low levels of TSH. Hyperthyroidism is rare in dogs; but they could be expected to have low TSH levels as well.
Old cats, showing no symptoms of hyperthyroidism, typically have lower TSH levels as well. We do not know if that indicates that those that do are at a higher risk of developing hyperthyroidism than those that do not.
The TSH test can also be in aid in seeing if forgetful clients have been regularly giving their pets the thyroid supplements they require. If they have, TSH levels should be low to normal. If they have been giving too much, just the opposite.
Complementary Tests :