Further investigations such as luteinizing hormone/follicle-stimulating hormone (LH/ FSH), Von Willebrand factor activity, and Ristocetin cofactor
assay were done in selected patients.
Von Willebrand factor ristocetin cofactor
(VWF: RCo) activity was measured with an in-house assay in a aggregometer (Chronolog Aggregometer 490) that measures the rate of aggregation of platelets in the presence of VWF and ristocetin.
Other assays in the HemosIL AcuStar VWF Assay Panel include: HemosIL AcuStar VWF Antigen (VWF:Ag) and HemosIL AcuStar VWF Ristocetin Cofactor
(VWF: RCo) Activity.
VWF activity (VWF: Ac, Innovance VWF Ac[R]) and ristocetin cofactor
activity VWF:RCo (BC von Willebrand Reagent[R]) both from Siemens Healthcare Diagnostics, Germany were measured according to the manufacturer protocol using the CS2100i coagulation analyser (Siemens Healthcare Diagnostics, Germany).
For test-associated errors, ristocetin cofactor
was associated with the highest variability and error rate, which was at least twice that using collagen binding.
Whole blood count, peripheral blood smear, blood group, ferritin, platelet function analyzer 100 (PFA-100), prothrombin time (PT), activated partial thromboplastin time (aPTT), thrombin time (TT), fibrinogen, von Willebrand factor antigen (VWF:Ag), VWF ristocetin cofactor
(VWF:RCo), factor VIII (F Viii), and platelet aggregation assays were performed.
1] To rule out coagulopathies, a structured history, Von Willebrand factor assay and ristocetin cofactor
assay may be done if necessary.
For patients needing vWF screening, a vWD profile was performed which included: aPTT, factor VIII quantitative functional assay, von Willebrand factor antigen (vWF:Ag) using latex immunoassay (Liatest--Diagnostica Stago-Paris/France), vWF ristocetin cofactor
(vWF: Rcof) (9,10) activity using vWFactor assay (Bio-Data-PA/USA), and ristocetin induced platelet aggregation (RIPA) using platelet aggregometry (Bio-Data-PA/USA ).
Although a history of vWD was reported only by the family of infant A (Table), testing at CDC's hemostasis laboratory revealed that both infant A and infant B had laboratory evidence of vWD, and infant D had borderline yon Willebrand factor antigen and ristocetin cofactor
results consistent with a vWD diagnosis.
The prothrombin time, partial thromboplastin time, plasma fibrinogen concentration, von Willebrand factor antigen concentration, Factor VIII activity, and ristocetin cofactor
activity were all normal.
For more than two decades, the ristocetin cofactor
(RCo) assay, which measures the vWF-mediated agglutination of platelets in the presence of the antibiotic ristocetin, has been the most common method for measuring the functional activity of vWF.
Patients with von Willebrand disease may have decreased VWF antigen, decreased ristocetin cofactor
activity, decreased ristocetin aggregation, decreased factor VIII levels, normal or increased APTT, and increased bleeding times with normal platelet counts.