Background Information Autoimmune thyroiditis (Hashimoto's Disease) 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. Hence, dogs may be clinically normal for years, only to become hypothyroid at a later date. The markers for autoimmune thyroiditis, autoantibody formation (autoantibodies to thyroglobulin, T4 or T3), occur prior to the occurrence of clinical signs. The majority of dogs that develop autoantibodies have them by 3 to 4 years of age. Development of autoantibodies at any time in the dogs life is an indication that the dog, most likely, has the genetic form of the disease.
As a result of the variable onset of the presence of autoantibodies, periodic testing will be necessary. Dogs that are negative at 1 year of age may become positive at 6 years of age. Hence, dogs should be tested every year or two in order to be certain that they have not developed the condition. Since the majority of affected dogs will have autoantibodies by 4 years of age, annual testing for the first 4 years is recommended. After that, testing every other year should suffice. Unfortunately, a negative at any one time will not guarantee that the dog does not have Hashimoto's disease.
The registry data can be used by breeders in determining which dogs are best for their breeding program. Knowing the status of the dog and the status of the dog's lineage, breeders and genetic counselors can decide which matings are most appropriate for reducing the incidence of Hashimoto's disease in the offspring.
General Procedures
Purposes
To identify those dogs that are phenotypically normal for breeding programs and to gather data on the genetic disease - autoimmune thyroiditis (Hashimoto's Disease).
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 enclosed application and general information instructions. The laboratory fee will be determined by the approved laboratory.
Certification
A certificate and breed registry 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. The OFA fee is $15.00 and no charge will be made for recertification at a later age. 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 a 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 data bank. Information on dogs determined to be abnormal (positive or equivocal) will not be made public without the explicit permission of the owner or agent.
Thyroid abnormalities fall into several categories
Two types will be defined by the registry.
a. Autoimmune Thyroiditis (Hashimoto's Disease).
b. Idiopathic Hypothyroidism
Autoimmune thyroiditis is known to be heritable.
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 3-6 months.
Classification
The method for classifying the thyroid status will be accomplished using state of the art assay methodology.
Indices of thyroiditis:
1. Free T4 by dialysis (FT4D) - This procedure is considered to be the "gold standard" for assessment of the thyroid's production and cellular availability of thyroxine.
2. Canine Thyroid Stimulating 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 and the pituitary gland functions normally. TSH is expected to be abnormally elevated in dogs with thyroid atrophy from autoimmune thyroiditis.
3. Thyroglobulin Autoantibodies (TgAA) - This procedure is an indication of the presence of the autoimmune process in the dog's thyroid.
CERTIFICATION
a. Normal, FT4D, 8-30pmoVL
cTSH, 7-40 mU/L
TgAA Negative
b. Positive advanced autoimmune thyroiditis
FT4D, <8pmol/L
cTSH, >40mU/L
TgAA Positive
c. Positive compensating autoimmune thyroiditis
FT4D, 8-30 pmoVL
cTSH 10-100 mU/L
TgAA Positive
d. Positive idiopathic hypothyroidism
FT4D, <8pmoVL
cTSH >40mU/L
TgAA Negative
Laboratory Certification
The laboratory certification process will include quality control, quality assurance and reagent certification.
Laboratories may apply and if successful will be approved to perform analyses for OFA thyroid certification. A site visit by a qualified veterinary endocrinologist chosen by OFA will be required and continued quality assurance and quality control will be necessary to maintain certification. Fully certified status can be obtained by passing the site visit and passing the results of the first OFA quality assurance assay result test.
The approved laboratory must be contacted for the appropriate submission forms, sample handling procedures and laboratory service fee before collecting the sample. Currently, samples may be submitted to:
Canada
Animal Health Laboratory
University of Guelph
Bldg. 49, McIntosh lane
Guelph, Ontario Canada N1G 2W1
519-824-4120 ext. 54500
United States
Animal Health Diagnostic Laboratory
B629 W. Fee Hall-B
Michigan State University
Lansing, MI 48824-1315
517-353-0621
Diagnostic Laboratory
New York State College of Veterinary Medicine
Cornell University, Upper Tower Rd
Ithaca, NY 14851
607-253-3673
Veterinary Diagnostic Laboratory
Attn: Sample Handling
College of Veterinary Medicine
University of Minnesota
1333 Gortner Ave
St. Paul, MN 55108
612-625-6782
University of California
Veterinary Medical Teaching Hospital
Clinical Pathology, Chemistry, Room 1017
1 Garrod Drive
Davis, CA 95616
530-752-7380
Texas Veterinary Medical Diagnostic Laboratory
1 Sippel Rd
College Station, TX 77843
409-845-3414
Other laboratories will be approved at a later date.
Azarel Shetland Sheepdogs
Quesnel, British Columbia, Canada
