Utilizing the Thyroid Database at OFA

 

 
 
 

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.

The majority of dogs that develop autoantibodies have them by 3 to 4 years of age. Development of autoantibodies to any time in the dog’s life is an indication that the dog, most likely, has the genetic form of the disease. Using today's technology only a small fraction of false positive tests occur.

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. Dogs should be tested every year or two in order to be certain 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 will not develop thyroiditis.

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 dogs lineage, breeders and genetic counselors can decide which matings are most appropriate for reducing the incidence of autoimmune thyroiditis in the offspring.

General procedures for using the Thyroid Database at OFA

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: A breed database number of 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 the 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 results determined to be positive or equivocal will not be made public without explicit written permission of the owner.

Thyroid abnormalities fall into several categories—two types will be defined by the registry.

  • Autoimmune Thyroiditis – Known to be heritable
  • Idiopathically Reduced Thyroid Function –Of unknown origin

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.

Classification

The method for classifying the thyroid status will be accomplished using state-of-the-art assay methodology.

Indices of thyroiditis:

  • Free T4 by dialysis (FT4D) — this procedure is considered to be the "gold standard" for assessment of thyroid's production and cellular availability of thyroxine. FT4D 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.

Normal:
FT4D within normal range
cTSH within normal range
TgAA is negative

Positive autoimmune thyroiditis:
FT4D less than normal range
cTSH greater than normal range
TgAA is positive

Positive compensative autoimmune thyroiditis:
FT4D is within normal range
cTSH is greater than or equal to normal range
TgAA is positive

Idiopathically reduced thyroid function:
FT4D is less than normal range
cTSH greater than normal range
TgAA is negative

All other results are considered equivocal

Approved Thyroid Labs: The laboratory certification process will include quality control, quality assurance and reagent certification. Laboratories may apply and, if successful, will be approved to perform analysis for OFA thyroid certification. A site visit by a qualified veterinary endocrinologist chosen by the 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. (There are approved laboratories at Michigan State University; Texas A&M University; Cornell University; University of Minnesota; University of California-Davis; University of Guelph, Ontario; Vita-Tech, Ontario; and Antech, Lake Success, NY. (Note that note that only the Lake Success, NY location is approved for Antech Diagnostics.)

Two milliliters (2mL) of serum are needed for testing. The serum sample must be from freshly collected blood..

Female dogs should not be tested during an estrus cycle.

Test results will be mailed or faxed only to the submitting veterinarian and the OFA. Results will not be available from the laboratory by telephone. The OFA will send a report to the owner.

The Animal Health Diagnostic Laboratory at Michigan State University has the largest pooled database on breed prevalence of autoimmune thyroiditis.

Michigan State University Thyroid Statistics

Note: Statistics from tests performed through 2004

Breed

Rank

Number of Evaluations

Percent Autoimmune Thyroiditis

Percent Equivocal

ENGLISH SETTER

1

1335

33.5

8.2

POLSKI OWCZAREK NIZINNY

2

75

30.7

8.0

HAVANESE

3

129

25.6

3.9

OLD ENGLISH SHEEPDOG

4

848

22.8

6.6

BOXER

5

7945

19.7

4.7

AMERICAN PIT BULL TERRIER

6

1171

19.6

7.0

GERMAN WIREHAIRED POINTER

7

313

19.5

7.7

TIBETAN TERRIER

8

266

19.2

10.2

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Adapted from “The use of health databases and selective breeding, A guide for dog and cat breeders and owners,” 4th edition, 2003, by Greg Keller, DVM, MS, DACVR. Published by Orthopedic Foundation for Animals, Inc. Reprinted with permission.