Von Willebrand disease laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Laboratory Findings
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 as 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.
Other tests performed in any patient with bleeding problems are a complete blood count (especially platelet counts), APTT (activated partial thromboplastin time), prothrombin time, thrombin time and fibrinogen level. Testing for factor IX may also be performed if hemophilia B is suspected. Other coagulation factor assays may be performed depending on the results of a coagulation screen. Patients with Von Willebrand disease will typically display a normal prothrombin time and a variable prolongation of partial thromboplastin time.