Thyroid Exam
What is Hypothyroidism?
With Hypothyroidism, the thyroid gland is not making enough of a hormone called thyroxine that controls metabolism (the process of turning food into fuel). Hypothyroidism causes a wide variety of symptoms, but is often suspected in dogs that have trouble with weight gain or obesity and suffer from hair loss and skin problems. The good news is this disease isn’t life-threatening, it’s easy to diagnose with a blood test, and it’s fairly easy and inexpensive to treat. Treatment is typically a thyroid supplement taken daily.
Autoimmune thyroiditis is the most common cause of primary hypothyroidism in dogs. The disease has variable onset, but tends to clinically manifest itself at 2 to 5 years of age. Dogs may be clinically normal for years, only to become hypothyroid at a later date. The marker for autoimmune thyroiditis, thyroglobulin autoantibody formation, usually occurs prior to the occurrence of clinical signs. Therefore, periodic retesting is recommended.
Thyroid Classifications
The method for classifying the thyroid status will be accomplished using state-of-the-art assay technology.
Indices of Thyroiditis
Free T4 (FT4) — this procedure is considered to be the “gold standard” for assessment of thyroid’s production and cellular availability of thyroxine. FT4 concentration is expected to be decreased in dogs with thyroid dysfunction due to autoimmune thyroiditis.
Canine Thyroid Simulating Hormone (cTSH) — this procedure helps determine the site of the lesion in cases of hypothyroidism. In autoimmune thyroiditis the lesion is at the level of the thyroid gland and the pituitary gland functions normally. The cTSH concentration is expected to be abnormally elevated in dogs with thyroid atrophy from autoimmune thyroiditis.
Thyroglobulin Autoantibodies (TgAA) — this procedure is an indication for the presence of the autoimmune process in the dog’s thyroid.
Certification Free T4 (FT4) Canine Thyroid Simulating Hormone (cTSH) Thyroglobulin Autoantibodies (TgAA)
Normal Normal range Normal range TgAA negative
Positive Autoimmune
Thyroiditis FT4 < normal cTSH > normal TgAA positive
Positive Compensative
Autoimmune Thyroiditis FT4 normal cTSH >/= normal TgAA positive
Idiopathically Reduced
Thyroid Function FT4 < normal cTSH > normal TgAA negative
All other results are considered equivocal.
OFA Thyroid Procedures
Purpose:
To identify those dogs that are phenotypically normal for breeding programs and to gather data on the genetic disease autoimmune thyroiditis.
Examination and Classification
Each dog is to be examined by an attending veterinarian and have a serum sample sent to an OFA approved laboratory for testing according to the application and general information instructions. The laboratory fee will be determined by the approved laboratory. All OFA forms and the OFA fee are submitted with the sample to the approved lab. Check with the referral laboratory for special sample handling and tests for registry purposes.
Certification
An OFA number will be issued to all dogs found to be normal at 12 months of age. Ages will be used in the certification process since the classification can change as the dog ages and the autoimmune disease progresses. It is recommended that reexamination occur at ages 2, 3, 4, 6, and 8 years.
Preliminary Evaluation
Evaluation of dogs under 12 months of age can be performed for private use of the owner since few dogs are already positive at that age. However, certification will not be possible at that age.
Dogs with Autoimmune Thyroiditis
All data, whether normal or abnormal is to be submitted for purposes of completeness. There is no OFA fee for entering an abnormal evaluation of the thyroid into the database. Information on results determined to be positive or equivocal will not be made public without explicit written permission of the owner.
Thyroid Abnormalities
Thyroid abnormalities fall into several categories - two types will be defined by the registry.
Autoimmune Thyroiditis (known to be heritable)
Idiopathically Reduced Thyroid Function
Equivocal Results
Those dogs with laboratory results that are questionable, therefore not definitive, will be considered as equivocal. It is recommended that the test be repeated in three to six months.