A rare blood clotting disease in Kerry Blue Terriers
This interesting information took place on KerryBlues-L, a newslist for Kerry Blue Terrier fanciers. Kathy Ericksen had a few questions about testing for von Willebrands disease before a Kerry goes in for surgery. The questions were answered by Daryl Enstone (denstone@SCIBORG.UWATERLOO.CA).
How is the vWD test performed?
It is a blood test. Kerries are affected by type I vWD and a blood test is the only one currently available. Certain breeds such as Scotties, Dobies, Manchesters and Shelties are affected by type III vWD and these breeds currently have a molecular genetic test available for their use. (See http://www.vetgen.com)
Is this a "routine" procedure?
No, not in a regular health check or pre-of procedure, unless the vet was actively suspicious that there was a problem. You would need to ask for it, unless there were symptoms present. Or unless the vet had dealt with a vWD positive Kerry before.
Does the test look for only vWD, or other genetic anomalies as well?
The vWD test only looks at the level of the von Willebrands factor in the blood. You would need to ask if you wanted to also test for, say, factor XI deficiency. A separate assay would be needed to determine the factor XI protein in the blood sample.
Does one need to request this test before surgery?
If you have a particular reason to worry that your dog may be affected with vWD (bruises easily, develops hemotomas, tends to bleed more than expected from cuts, etc.) then it would be worth discussing with a vet before surgery.
A lot of "test-bashing" goes on over the vWD blood test. Many people consider the test unreliable because the test results can be very variable, sometimes indicating that a dog is vWD positive and sometimes vWD clear. This is sometimes the case with borderline cases. The test must also be carried out with a great deal of care. von Willebrands factor is a protein - the largest circulating protein in the body - and it is quite delicate, i.e., it is easily damaged in the sampling procedure. The more protein is damaged during testing, the lower (falsely) the test result will be.
Some suggestions from Dr. Dodds in obtaining a "good" sample:
- Make sure the dog is healthy and unstressed and between heat cycles and not lactating (for females) when the test sample is taken. Stress, even the stress of having a second vial of blood drawn, will lower the level of vWfactor. Thyroid deficiency can also lower vWf levels.
- To prepare a "duplicate" for the test, do not take separate samples from different veins. Instead use one sample, centrifuge and remove the plasma, *mix it thoroughly*, then divide it into two portions. If the centrifuged plasma is not mixed thoroughly, the top portion of the plasma will be lower in vWf than the lower portion simply because of the centrifugation step (i.e., the vWf protein, being relatively big and heavy, will have sunk to the bottom).
- Draw blood directly into a Vacutainer. Do not draw blood with a syringe and then empty it into a Vacutainer. Using a dry, empty syringe will allow the clotting process to begin before the blood is exposed to the anticoagulant in the Vacutainer. This can produce inaccurate (falsely low) results. Citrate is specifically named as the anticoagulant type.
- Samples must remain cold or frozen in transit. An overnight delivery system is required. Always use an insulated container with a cold pack, even in winter, to protect against exposure to heating units.
This information comes from:
Inherited and acquired von Willebrand's Disease, Part 1. W.J. Dodds, S.L. Raymond & M.B. Brooks. Veterinary Practice Staff 5 (4) 1993, pp. 1, 14-17.