von Willebrand Disease Flashcards
what is the most common inherited bleeding disorder?
von willebrand disease
what is von willebrand disease?
caused by a deficiency or a defect in von Willebrand factor (vWF)
when vWF is deficient or does not function properly, blood clotting is impaired
describe the defect in von Willebrand disease
the defect in von Willebrand disease may be quantitative (not enough von Willebrand factor is made) or qualitative (an abnormal form of von Willebrand factor is made)
both types of defects may impair hemostasis and result in an increased bleeding tendency
what are the two major functions of vWF?
- it binds platelets to the subendothelium in a process called platelet adhesion
- it binds and stabilizes factor VIII in the circulation
where is vWF found?
subendothelial cells and platelets
what does vWF do when a blood vessel is damaged?
collagen is exposed to the circulating blood, and von Willebrand factor acts as the glue that adheres platelets to exposed collagen via platelet glycoprotein Ib (GpIb) receptors
what is vWF more important job?
In most cases of von Willebrand disease, the role of vWF in mediating platelet adhesion is much more important than any potential deficiencies in factor VIII
but in a small number of cases of von Willebrand disease, the decrease in available factor VIII is so pronounced that the disease mimics hemophilia A
hemophilia A is a hereditary disease in which factor VIII is decreased or absent
what is the clinical presentation of vWF?
varies in severity but most cases do not cause clinically significant symptoms
even when symptoms are present, clinical manifestations are usually mild and non-life threatening
symptoms include easy bruising, bleeding from mucous membranes (frequent nosebleeds), excessive bleeding from wounds, petechiae, and menorrhagia
what tests can you do to test for vWF disease?
- quantitative tests are used to measure the quantity, size, and function of vWF and factor VIII
- a von Willebrand factor antigen assay may be used to measure the amount of vWF in the blood
- function of vWF can be measured using the ristocetin platelet agglutination test***
- look at PPT because if factor VIII is decreased, the PTT will be prolonged
Why might many cases of von Willebrand disease go undiagnosed?
Cases of vWD can have very mild symptoms that result in only a slight increase in bleeding tendency. A person with vWD may only notice that they bruise a bit more easily or get frequent nosebleeds and have no other significant symptoms.
what is type 1 vWD?
autosomal dominant
most common type of vWD
low levels of vWF in circulation
what is type 2 vWD?
there are normal amounts of vWF but vFW does not function properly
has 4 subtypes: A,B,M,N
types 2M and 2N are really rare
what are the characteristics of type 2A and B vWD?
relate only to the high molecular weight form of vWF
these are large multimers of vWF and are the most active form of vWF
changes in quantity or function of this particularly active, high molecular weight form will have a large impact on platelet adhesion to damaged blood vessels and factor VIII stability
what is type 2A vWD disease?
it’s a a result of a decrease in the amount of high molecular weight vWF in circulation
vWF is still being produced, but the loss of the most active form of vWF results in an overall decrease in vWF activity
what is type 2B vWD disease?
caused by “hyperfunctional” high molecular weight multimers that cause spontaneous aggregation of platelets leading to symptoms similar to thrombotic thrombocytopenic purpura (TTP)
these spontaneous aggregations of platelets use up much of the available vWF resulting in low levels of the factor
