Canine Hypothyroidism Diagnosis
As symptoms of the disease can be incredibly variable and almost contradictory, if a dog is suspected of having hypothyroidism then this means that several symptoms are evident, all simultaneously.
The only way to be sure of proper diagnosis, depending on the type of symptoms is one of the following hormone tests which would be carried out by your vet.
The thyroid hormones T3 and T4 (the most common) would be tested, along with a test for autoimmune thyroiditis, by searching for antibodies.
The latter is the genetic form of this disease.
For the T4 test, blood is tested by radioimmunoassay which will determine T4 levels in the bloodstream.
If this test proves positive, because other factors may cause lowering of T4 levels a more precise test would usually be done.
The baseline T3 test is a screening test which will sometimes be used instead of a T4 test.
However, T3 testing in early stages of hypothyroidism may prove inaccurate, therefore it is rarely used to make sure of accurate diagnosis in all stages.
Testing of TSH (thyroid stimulating hormone) levels could also be carried out to measure blood TSH levels.
A dog with a high level, would indicate hypothyroidism because the body is producing stimulating the thyroid gland to create more thyroid hormone.
The next test is the thyroid stimulation test (TSH stimulation test).
This is usually carried out when low T3 or T4 levels are found, which will confirm prognosis.
In this test, thyroid stimulating hormone will be injected into the dogs vein and then after several hours a new blood sample will be collected and T4 levels checked once more.
If the T4 levels have not increased from the original blood sample, this will indicate that the dog is positive for hypothyroidism.
Because T4 can be found in two forms, the 'bound' form (attached to proteins and can't enter cells) and the 'free' form (enters cells) the laboratory test called Equilibrium dialysis, was designed to accurately measure the free form T4 hormone levels.