Willebrand disease is the most common hereditary coagulation abnormality described in humans, although it can also be acquired as a result of other medical conditions. It arises from a qualitative or quantitative deficiency of von Willebrand factor , a multimeric protein that is required for platelet adhesion. It is known to affect humans and dogs. There are four types of hereditary WD. Other factors including ABO blood groups may also play a part in the severity of the condition. A bleeding disorder characterised by prolonger bleeding time.
* Recurrent blood noses * Bruising * Bleeding gums * Menorrhagia * Gastrointestinal bleeding
Unlike hemophilia, von Willebrand’s disease is inherited as an autosomal dominant trait that affects males and females equally. One theory of pathophysiology holds that mild to moderate deficiency of factor VIII and defective platelet adhesion prolong coagulation time. Specifically, this results from a deficiency of the vWF, which stabilizes the factor VIII molecule and is needed for proper platelet function. Defective platelet function is characterized by: ❑ decreased agglutination and adhesion at the bleeding site ❑ reduced platelet retention when filtered through a column of packed glass beads ❑ diminished ristocetin-induced platelet aggregation. Recently, an acquired form has been identified in patients with cancer and immune disorders.
When suspected, blood plasma of a patient needs to be investigated for quantitative and qualitative deficiencies of vWF. This is achieved by measuring the amount of vWF in a vWF antigen assay and the functionality of vWF with a glycoprotein (GP)Ib binding assay, a collagen binding assay or, a ristocetin cofactor activity (RiCof) or ristocetin induced platelet agglutination (RIPA) assays. Factor VIII levels are also performed because factor VIII is bound to vWF which protects the factor VIII from rapid breakdown within the blood. Deficiency of vWF can therefore lead to a reduction in factor VIII levels. Normal levels do not exclude all forms of vWD: particularly type 2 which may only be revealed by investigating platelet interaction with subendothelium under flow (PAF), a highly specialized coagulation study not routinely performed in most medical laboratories. A platelet aggregation assay will show an abnormal response to ristocetin with normal responses to the other agonists used. A platelet function assay (PFA) will give an abnormal collagen/adrenaline closure time and in most cases (but not all) a normal collagen/ADP time. Type 2N can only be diagnosed by performing a "factor VIII binding" assay. Detection of vWD is complicated by vWF being an acute phase reactant with levels rising in infection, pregnancy and stress.
* Hematology (Blood Specialists) * Pediatric Hematology / Oncology (Child Cancer/Leukemia) * Hematopathology