What Are the Most Important Thyroid Tests That Need to Be Done?

Posted on July 15th, 2016

For some reason, the veterinary profession measures thyroid function, only with levels of thyroxin (T4).

Many times these same T4 levels are also measured for free amounts of thyroxin (free T4).

My concern deals with the fact, that only that they are only asking to measures T4 (Thyroxin), which may not diagnose a thyroid imbalance, without also measuring T3 (Triiodothyronine).

For your own information, T4 in my opinion, is a type of storage thyroid hormone, that needs to be transferred into T3, which is the active form of thyroid hormone.

The literature does indicate, that T4 is a thyroxin hormone, that does contain iodine, which is derived from the amino acid tyrosine.

With more sophisticated testing, iodine and tyrosine may be tested for, mainly in humans.

Many cruciferous vegetables, unless cooked, will bind tyrosine.

For more information on different cruciferous vegetables,

please either go to the internet with my name, or stay on this website and read,

Common Foods That May Suppress Thyroid Function in You and Your Pet.

The literature further indicates that the tyrosine produces the L-Thyroxin.

Its chemical name for the l-Thyroxin, is Tetraiodothyroxin. It if formed, and stored in the thyroid follicles.

The T4 is changed in the tissue, into T3 (triiodothyronine), which is much more, biologically active.

My question for you and your veterinarian is, why are not both T3 and T4 measured, when you are concerned about a patient, with a possible thyroid


In human patients, a Thyroid Stimulating Hormone (TSH) is also measured, which should be very low, otherwise the pituitary indicates that increased amounts of T3 and T4, are needed, to be produced.

My own studies in humans, which I was allowed to do by their MD’s, indicated when the adrenal estrogen is elevated, it causes the production of a Thyroid Binding Globulin (TBG), and when this happens, a patient can have normal levels of T3 and T4, but the TBG makes these thyroid hormones unavailable for use, in the body.

This indicates that you can still be hypothyroid, with normal levels of T3 and T4.

My studies in animals and in humans, also indicates that it takes normal amounts of active cortisol to transfer T4 into T3, which may be part of the tissue transference, from T3 to T4

Please realize that a cortisol level by itself, unless it is deficient, will NEVER indicate if that cortisol is functional or non-functional, without first measuring adrenal estrogen. Unfortunately, this is really not understood, just yet.

NOTE: These are all part of my clinical studies that are not understood.

When a diagnosis of hyperthyroidism is made with a feline or canine patient, merely based upon an elevated T4 level, the patient may still not be hyperthyroid.

You definitely need to know what the T3 level is.

If both the T3 and T4 levels are elevated, there is a good chance that the feline or canine has hyperthyroidism.

However, if the T4 is elevated and the T3 is normal or deficient, the patient does not have hyperthyroidism, but rather a cortisol imbalance and will need to be treated for the cortisol imbalance, and NOT, for hyperthyroidism.

For further information on the estrogenic adrenal effect on the thyroid hormones, please go to the internet with my name or stay on this website, and read, The Estrogen’s Vicious Cycle

Hopefully this article will shed some light on thyroid function and help you make the proper decision on how to treat your dog or cat, with a thyroid imbalance.

Always ask that a T3 level be included with a T4 level.


Dr. A. J. Plechner