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He wants to do another draw in 3 months.
The more reading I do the more I understand how hard it is to accurately diagnosis hypothyroidism.
Personally I would not wait 3 months to get a full thyroid panel. A low total T4 can be a protective mechanism caused by illness and does not necessarily indicate a poorly functioning thyroid gland. I am assuming that T4 is the one thyroid number you currently have and (by itself) all that number tells you is that you need to do further tests.
I would hate to see you cover up another illness by supplementing a perfectly normal thyroid gland which the body has signaled to slow down. If you don't read anything else in the article below, read the last paragraph.
Frankly, I would talk to Dr. Dodds (Hemopet). She may want you to stop the supplementation, wait a period of time, and then do the full thyroid panel.
A Diagnostic Dilemma
http://rivercitypetwatch.com/files/Diagnostic_dilemma.htm
"Every year, thousands of dogs are diagnosed with hypothyroidism and most subsequently receive lifelong thyroid supplementation. But many of these dogs do not have the disease. ...
When the body experiences altered demands and priorities such as illness or stress, the thyroid gland tries to compensate by minimizing energy requirements. Energy is conserved by reducing thyroid hormone secretion. This, in turn, lowers the body's metabolic rate. ...
SES (sick euthyroid syndrome) describes the situation in which dogs with normally functioning thyroid glands have decreased thyroid hormone levels with an appropriate cause. Virtually any condition trauma, stress, injury, illness, poor diet can affect thyroid hormone levels and cause SES.
SES is actually a protective mechanism. When the body experiences altered demands and priorities such as illness or stress, the thyroid gland tries to compensate by minimizing energy requirements. Energy is conserved by reducing thyroid hormone secretion. This, in turn, lowers the body's metabolic rate.
Further compounding the problem is that whatever initiates SES may be vague and difficult to identify. Without comprehensive diagnostics and evaluation, low thyroid hormone levels may be the most obvious abnormality, leading to a misdiagnosis of hypothyroidism.
If a dog with SES is misdiagnosed and is supplemented with thyroid hormone, the body's protective mechanism can be negated.
... high cholesterol after a fast supports a diagnosis of hypothyroidism, but it is not definitive.
Another diagnostic clue is that as many as 40 percent of hypothyroid dogs have anemia - decreased numbers of red blood cells without signs of replenishment. This finding also supports a diagnosis of hypothyroidism, but again, is not definitive. Other causes of anemia should be considered.
Abnormalities in the urinalysis suggest a problem other than hypothyroidism. ...
A total T4 result far below normal or near zero strongly suggests true hypothyroidism. Still, more definitive testing is highly recommended before committing a dog to a lifetime of thyroid supplementation and monitoring. Though a popular test, total T4 is a poor method for evaluating thyroid function. It is limited because many uncontrollable factors affect total T4 levels. ... Even ambient temperature can affect a diagnosis - a car ride to the vet's office on a hot summer day may decrease total T4 levels, causing false low results. ...
To what degree various factors affect total T4 remains unknown. But it is clear that a diagnosis of hypothyroidism based solely on the results of total T4 is seriously flawed. It is subject to tremendous error, which can lead to the inappropriate treatment of many dogs.
Aside from the limitations described, measuring total T, and total T4 neglects to evaluate thyroid function. Because inadequate thyroid function is the distinguishing characteristic of a truly hypothyroid dog, a thyroid function test is imperative for proper diagnosis. ...
The take-home message is this: Lifelong thyroid supplementation for a diagnosis of hypothyroidism based on a total T4 and an apparent response to treatment is perhaps the single greatest reason for misdiagnosis and over treatment. Many diseases may respond to thyroid supplementation in the absence of hypothyroidism. Because a non-thyroid disease seems to improve with thyroid supplementation does not signify a cure, a treatment or, for that matter, even a benefit."