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Von Willebrand

by Francois-R. Bernier

Based on Fact Sheet by Marjorie Brooks, DVM, Dip.ACVIM Comparative Coagulation Section Diagnostic Lab, Cornell University

This refers to the von Willebrand factor antigen test by ELISA which is reported as a % vWF:Ag compared to a pooled sample of normal plasma given a value of 100. Von Willebrand is a bleeding disorder caused by a deficiency of von Willebrand factor protein. This protein circulates in the blood stream and is involved in the first phase of blood vessel repair in response to vessel injury. Von Willebrand disease is not the same as hemophilia.

Severity of bleeding is highly variable in dogs affected with vWD. In general, spontaneous bleeding tends to occur from mucous membranes lining the nose, mouth, urinary, reproductive and intestinal tracts. Excessive bleeding in puppies may be noted after tail docking, dewclaw removal, tattooing, or when the pup is teething. In less severely affected dogs, abnormal bleeding is seen only after surgery or trauma. Concurrent stress conditions (....) can all exacerbate signs of hemorrhage in dogs affected with vWD. Ranges for plasma v WF:Ag established at Cornell are as follows: Normal Range 70 to 180% , Borderline 50 to 69 % , Abnormal Range 0 to 49%

Normal range was previously considered to be 60 to 180 but a few cases were found of dogs with results in the 60% range that proved to be carriers, so that the normal range floor was raised to 70%. Dogs testing in the 70-180% range are considered clear of vWD and at low risk for expressing or transmitting vWD. Dogs in borderline range cannot be accurately classified as carrier or clear of the trait based on that measurement. This is an overlap region of plasma vWF:Ag, where most individuals are clear, but some are carriers of vWD. On a second test, some borderline range individuals fall in the normal or abnormal range, thereby enabling a prediction of their genetic status treated as carriers and dogs in abnormal range are considered as carriers. Dogs testing in the abnormal range are considered carriers and are at risk for transmitting an abnormal vWF gene to offspring.

On my dogs that have been tested I have gotten results ranging from Dash with a 69% vWF:Ag to her granddaughter Wager at 102% vWF:Ag. Amy the Shorthair was at 115% vWF:Ag.

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