OFA Thyroid Certification
Three specific tests will be performed, Free T4 by Dialysis (FT4D), Canine Thyroid Stimulating Hormone (cTSH) and Thyroglobulin Autoantibodies (TgAA). FT4D is a measurement of T4, (thyroid hormone) which is circulating in the dog’s bloodstream. You may be familiar with the T4 test, but used alone a T4 is not considered a reliable way to assess a dog’s thyroid status. Non-thyroidal illnesses may suppress the T4, causing falsely lowered results, and antibodies against T4 may adversely affect the test, causing falsely elevated results. FT4D is the most current and accurate method of measuring a dog’s T4 status, and is considered the “gold standard” for assessment of available T4 in the bloodstream. FT4D values increase artificially if the sample is not properly handled, so the blood sample must be prepared soon after it is drawn from the dog, refrigerated and sent to the lab by an overnight delivery service.
Thyroid Stimulating Hormone (TSH) is a substance produced by the pituitary gland, a small part of the brain which functions to regulate various hormone systems in the body. If the pituitary detects that cells in the body need more thyroid hormone, it produces TSH, which in turn causes the thyroid gland to produce more thyroid hormone. If a dog has an elevated TSH, this is an indication that the cells in the body are not receiving enough thyroid hormone, regardless of the level of T4 measured. This is why measurement of T4 alone is no longer considered a reliable indicator of thyroid function. Measurement of TSH has been considered an important part of thyroid function assessment in humans for years, but a test to measure levels of TSH only recently became available in the dog. Measurement of canine TSH (cTSH), in combination with T4 levels, is now considered the standard for assessing thyroid function status in dogs.
A low T4, in combination with an elevated cTSH, is considered diagnostic of hypothyroidism (low thyroid function) in dogs. A low T4 with a normal cTSH may indicate that the T4 was falsely lowered, perhaps by some other disease process in the animal, while a normal T4 and an elevated cTSH may indicate a dog that is hypothyroid, despite his normal T4 level. It is possible that the dog has antibodies against his own thyroid hormone that are preventing the T4 from actually doing its job in the cells, or it is possible that the dog may have a defect that prevents the T4 from being properly taken up by the cells, so that even thought there is circulating T4 in the bloodstream, it isn’t being properly utilized by the cells.
Most dogs are born with normal thyroid function, but many become hypothyroid as they age. One cause of this is autoimmune thyroid disease (Hashimoto’s disease). In this condition, the dog’s immune system becomes confused and starts creating antibodies against its own thyroid hormone. Autoimmune disease means that a dog’s immune system has incorrectly identified some substance in the body as a foreign intruder, and is creating antibodies directed against the dog itself (autoantibodies), rather than the bacteria, viruses, etc. against which they should be directed. Autoimmune thyroid disease is considered inherited in dogs, and autoantibodies may in some cases be detected before the dog has clinical signs of hypothyroidism. The third test in the OFA series, Thyroglobulin Autoantibodies (TgAA) detects antibodies which are incorrectly directed against the dog’s thyroid hormone.
The second major cause of hypothyroidism in dogs is idiopathic hypothyroidism. Idiopathic means that no one knows what causes it, and in idiopathic hypothyroidism, the dog’s thyroid gland simply stops producing hormones.
A dog will be certified as thyroid normal if all three of these tests are in the normal range. A dog with a low T4, an increased cTSH, and positive TgAA will be considered to have autoimmune thyroid disease. A dog with a normal T4, increased cTSH, and positive TgAA will be considered to have autoimmune thyroid disease which has been compensated for by the production of more T4 in response to destruction of some T4 by the antibodies, and the subsequent release of more cTSH. These dogs are considered to have an autoimmune disease, and would not be recommended as breeding stock. Dogs which have low T4, increased cTSH and are negative for TgAA are considered to have idiopathic thyroid disease.
If you are interested in having your dogs certified as thyroid normal, there are several procedures to follow. Ask your veterinarian to contact the OFA at (573) 442-0418 (fax 573-875-5073) and obtain the necessary forms. Also ask your veterinarian to contact the Diagnostic Laboratory at Michigan State University (517) 353-0621 (fax 517-353-4466) for information. Before sending samples, your vet must obtain an insulated shipping container, the proper canine thyroid registry form, and instructions for drawing and handling the blood sample.
Both sets of paperwork (and the appropriate fees) must be submitted at the time the blood is sent to the lab. In order to get an accurate study of the percentage of affected dogs, your veterinarian will not be allowed to send the blood to the lab and later send the paperwork to OFA. It must all be submitted at one time.
The OFA thyroid registry is the first “open” registry that OFA has established. The hip registry, for example, is a “closed” registry. This means only information about dogs with normal hips (those that are OFA certified) is released to the public. The disadvantage of a closed registry is that even though a breeder may know the status of a particular individual, there is no way to learn the status of that dog’s relatives, if their hips did not certify. This makes it much more difficult to make intelligent breeding decisions. In the “open” registry, information about both normal and abnormal dogs will be released, but ONLY if the owner gives their permission. One of the questions that must be answered on the OFA form for thyroid testing is whether the owner wants abnormal results to be released.
Let me take this opportunity to encourage you to share all your results, regardless of whether or not they are normal. Take advantage of this open registry, and encourage other breeders to do the same. Breeding a dog who is normal for an inherited condition, but who has affected siblings, to another dog with a similar status is not the way to reduce the incidence of a genetic disease. Only by working together, and sharing test results, can breeders effectively breed healthier dogs. For those of you who are wondering, “will she put her money where her mouth is?” the answer is yes. As I write this, I have two dogs with test results pending. I have agreed to have their results released regardless of the outcome. Should one of them (or any dog) have abnormal results, please don’t look upon this as an opportunity to start a witch hunt, but as an opportunity to learn more about what you are dealing with in any given pedigree.
OFA requires the dog to be at least one year old at the time of certification. However, the onset of hypothyroidism is usually 2-5 years, so like CERF testing for eyes, reexamination is necessary. OFA currently recommends 2,3,4,6 and 8 years of age. Dogs with borderline results should be retested in 3-6 months. Many medications and illnesses can affect these results. If your dogs are on any medications other than routine items such as heartworm preventative, you should wait to test the dog until it is healthy. The dog must not have had any type of thyroid medication for a period of three months prior to the test. If you have questions about the status of any of your dogs regarding testing, consult your vet, or ask them to confer with the doctors at the MSU lab.
One further note regarding certifications. For several years now, OFA and CERF certification numbers have appeared on both AKC registration papers and on official AKC pedigrees. In an effort to encourage breeders to permanently identify dogs, and among other things, reduce the potential for fraud in these certifications, AKC has announced that as of July 1, 1996, certifications will no longer be listed by the AKC if the dog was not permanently identified at the time of the test. Both OFA and CERF forms have a place to list the dog’s tattoo and/or microchip number. If you are having certification tests performed, be sure that your dog’s identifying info is included on the form. Previously published OFA and CERF info will be discontinued by the AKC on January 1, 1998, if the dog has not been permanently identified.
While tattooing/microchipping is not yet required for CERF/OFA, only for AKC publication, please consider permanently identifying your dogs. It will help with your AKC record keeping, will reduce the possibility of fraud, and may very well one day save your dog’s life.
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