My Basenji's T4
reading came back "low normal." I've heard that this is very low
for a Basenji. Should she be on thyroid supplementation?
Jennifer's response:
Unfortunately it's a bit more complicated than that! Any dog who is sick for virtually any reason (and stresses such as being newly adopted, moving, etc..) will have a low T4 (thyroid hormone) measurement even if they have completely normal thyroid function. There are ways to help sort out whether the T4 is low for this reason or whether the thyroid gland is really underproducing, but a simple total T4 measurement will not tell you this.
It's important to try to distinguish true hypothyroidism from this low T4 that we find with sickness or stress because once you start supplementing with thyroid hormones, that causes the dog's own thyroid glands to shut down and atrophy! In other words, you end up inducing a hypothyroidism that wasn't there to start with and the dog ends up having to take thyroid supplements for its whole life despite having normal functional thyroid glands. It's worth trying to find out for sure whether the glands are working right or not.
Determining whether a dog is really hypothyroid or not requires looking at and integrating a number of specific pieces of information, not just one. The thyroid gland works as part of a tightly interconnected system with the pituitary gland and hypothalamus and produces hormones which undergo conversions from one form to one of several others within the body, only one of which is actually usable by the body.
In addition, some thyroid hormone is bound by protein and unavailable for use by cells, some is freely available. In order to develop a full picture of thyroid function, all of these factors need to be considered.
In a full canine thyroid evaluation panel such as is available from Michigan State University, measurements are provided of total T4, total amounts of its biologically active relative T3, free T3 and T4, the presence of any antibodies against T3 or T4, as well as amounts of the pituitary hormone TSH, which is responsible for stimulating thyroid activity. Each of these is part of the total puzzle in sorting out thyroid function in an animal which has a low total T4. An initial in-clinic low total T4 value is merely suggestive of the fact that there may be a problem with thyroid function. To make a definitive diagnosis, further tests need to be run at special outside labs such as the one at Michigan State, with the results then carefully interpreted by the dog's veterinarian.
Article copyright © 2001 by Jennifer Yearley, DVM.
All rights reserved.