Thyroxine (T4) and Thyrotropin (TSH)

The measurement of thyroxine (T4) and thyrotropin (TSH) at a single point in time. It is important to know that a dog receiving Thyforon® therapy is absorbing the medication appropriately. Insufficient absorption or insufficient dose will lead to treatment failure and over-dose can lead to clinical signs of hyperthyroidism. When a T4 measurement is made, it is important to record the hours post-pill at which the sample was taken to be able to appropriately interpret the results.

Thyrotropin (TSH) levels take several days to change in response to changes in thyroxine (T4) therapy, they therefore are able to reflect the adequacy of therapy in the days preceding the test. TSH could be described as the “fructosamine of hypothyroidism”.

The combined measurement of T4 and TSH will help in the identification of compliance failure and reduce unnecessary dose adjustments that could arise from reliance on T4 measurement alone on an “unrepresentative” day.