Von Willebrand’s Disease (VWD) - Page 3

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Von Willebrand’s Disease (VWD)

By: Dr. Leah Cohn

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Diagnostic tests are needed to recognize vWD and exclude other diseases. Tests may include:

  • A complete history and physical examination. Breed, age and prior illness will be questioned.

  • A dog's breed will be considered if your veterinarian suspects vWD. Although any breed can be affected, certain breeds, such as the Doberman pinscher, Shetland sheepdog, schnauzer and golden retrievers are more likely to have vWD. German shorthaired and wirehaired pointers, Scottish terriers and Chesapeake Bay retrievers have been documented to have very rare but very severe forms of vWD.

  • A dog's age will be considered if vWD is suspected. Because this is a congenital disease (present from birth), dogs are often identified at the time of neutering or during early cosmetic surgery (ear cropping). Nonetheless, it is not uncommon for a dog with mild vWD to go undetected until later in life.

  • A complete medical history can lead your veterinarian to suspect vWD. A previously healthy dog that experiences prolonged bleeding after minor injury is a typical example of vWD. Certain rare forms of vWD can result in severe, life-threatening bleeding unassociated with injury.

  • A physical examination may prompt your veterinarian to consider vWD as a cause for abnormal bleeding. The type and location of bleeding may make platelet disorders, hemophilia or rodenticide intoxication more or less likely a cause of bleeding. Physical examination may also rule local disease out as a cause of bleeding.

  • A complete blood count (CBC) should be performed on any bleeding dog to make certain the number of platelets is normal and to check for anemia (a deficiency of oxygen-carrying red blood cells).

  • Tests of clotting ability, including Activated Partial Thromboplastin Time (APTT) and One-Stage Prothrombin Time (OSPT), may be requested in a bleeding dog. Although results of these tests will be normal in a dog with vWD, they help rule out other diseases, including hemophilia, warfarin toxicity (rat bait poisoning) and disseminated intravascular coagulation.

  • Buccal mucosal bleeding time is a screening test for vWD. A small, precise cut is made inside the dog's lip and the time it takes for a blood clot to form is measured. In dogs with vWD the time until a clot forms will be longer than normal. In addition to vWD, platelet deficiency or dysfunction and blood vessel disease may prolong bleeding times.

  • Specific testing involves sending blood samples to have vWF measured. The amount of vWF in the blood sample is compared to a pooled sample from a large group of healthy dogs. The results are expressed as a percentage of the normal pooled sample (exact percentages considered to constitute each range may vary slightly from laboratory to laboratory). If a dog is found to have greater than 70 percent as much vWF as the pooled sample, it is considered unaffected. Dogs with less than 50 percent of the amount of vWF in the pooled sample are considered to be affected. Dogs with 50 to 69 percent of the amount of vWF found in the pooled sample fall into a "borderline" range. von Willebrand's disease occurs in three subtypes. Type I vWD is by far the most common and the least severe. Types II and III vWD are relatively rare but cause much more severe bleeding episodes than Type I vWD.

  • Unfortunately, repeated measurement of vWF concentrations may be necessary, especially if the dog's values fall into the "borderline" range. There is considerable day-to-day variation in blood vWF concentrations. Factors like pregnancy, exercise, stress or illness can affect concentrations.

  • In dogs believed to have the rare but severe form of vWD known as Type II vWD, electrophoresis can be used to measure the size of the vWF present. Type II vWD, found most often in German shorthaired and wirehaired pointers, is associated with a loss of only the large pieces of vWF.

  • Genetic testing for vWD is available for some breeds of dog, including Doberman pinschers, Scottish terriers, poodles, Manchester terriers, Shetland sheepdogs and Pembroke Welsh Corgis.

  • If vWD is identified, your veterinarian may request testing for thyroid hormone status. An underactive thyroid gland (hypothyroidism) has been associated with vWD in some cases, and although controversial, correction of hypothyroidism may improve the vWD.

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