Hypothyroidism

What would you consider "normal" T4 levels for a Border Collie? If you had a Border Collie with a T4 of 0.8, along with a high cholesterol, would that automatically constitute hypothyrodism?

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Unfortunately, diagnosing hypothyroidism isn't so easy. Yes this is possible hypothyroidism, but it could be normal. Depends on several things. Since the thyroid gland affects the body in its entirety, diagnosis must also be done as a whole rather than a simple course of tests. Many of the effects are diffuse and easily confused with other problems (one reason why I think it is overdiagnosed). Skin problems and weight problems are most commonly overdiagnosed as hypothyroidism.

To figure out hypothyroidism, your vet needs to complete a thorough history of the dog. And followup must be accomplished to verify the diagnosis. Diagnosis is an ongoing process, not a one-step blood analysis. The only way to do it in a simplified manner is to either see the thyroid atrophy yourself (though this may not be so obvious) or if the test results are so far out of the normalized range, that any other conclusion would be preposterous.

There are several tests that can be used to determine hypothyroidism - so be certain which test your vet is giving. Many of them measure both T3 and T4 levels and we now know that T3 levels are pretty much useless in figuring out thyroid problems. T4 levels are the ones that count. Most of the tests determine a low resting T4 concentration but this isn't completely conclusive. Many drugs may artificially lower the baseline level, other diseases may do so as well, and there are breed issues, as in the Border Collie. These low levels need to be confirmed with a TSH stimulation test (TSH is administered to the dog then at a later point, blood is collected to see the change in concentration). This, in a way, measures the action of the thyroid gland, not simply a resting blood level of a thyroid hormone.

Several other factors may point to a possible thyroid problem:

weight gain (even though food is not increased or exercise reduced - though see the next one for complications of this)
lethargy, listlessness, general lack of enthusiasm (especially in a Border Collie)
loss of appetite
hair loss or thinning (especially on the body), usually symmetrical
"heat seeking missles" - hypothyroid dogs are constantly cold and seek out any warm place
skin problems - excessive dryness, thickening of the skin
puffiness in the face
high cholesterol

Altogether, these signs in conjunction with the thyroid blood levels can determine a problem with the thyroid. Taken separately, they may mean little or point to some other condition entirely. Once the dog is put on thyroid meds, followup must be done in order to determine if, in fact, it was thyroid problems. If the drugs don't correct the problems and blood serum levels are unchanged, then it was misdiagnosed. Thyroid problems do exist but it's not the only cause of these very diverse conditions. Thyroid blood tests are easy to conduct so they should be done in the beginning if hypothyroidism is suspected but that shouldn't be taken as the final word. Putting your dog on a lifetime drug should not be taken lightly nor with a simple series of tests.