Carbohydrate moiety of von willebrand factor is not necessary for maintaining multimeric structure and ristocetin cofactor
activity but protects from proteolytic degradation.
The laboratory tests of the patient were as follows: quantitative hCG 117740 IU/ml, TSH 3,229 [mu]IU/ml, and free T3 and T4 were within normal ranges; hemoglobin 16,7 g/dl, hematocrit 47,6%, E2 >5000 pg/ml, PT, PTT, and fibrinogen were within normal limits; routine biochemical tests were normal (for example, total protein, albumin, creatinine, BUN, Na, K, AST, ALT, and LDH); interestingly CA-125 (564 IU/mL) was found higher, Inhibin A 861, Ristocetin cofactor
(von Willebrand factor (VWF) activity) 100% (50-100%), and VWF antigen 150% (60-150%).
Further investigations such as luteinizing hormone/follicle-stimulating hormone (LH/ FSH), Von Willebrand factor activity, and Ristocetin cofactor
assay were done in selected patients.
Laboratory evaluation confirmed type 1 VWD with ristocetin cofactor
activity of 38%, von Willebrand antigen level of 41%, factor VIII level of 60%, and a normal von Willebrand factor multimer distribution.
Von Willebrand studies were normal (Von Willebrand factor [VWF] antigen, 112 IU/dL; ristocetin cofactor
, 120 IU/dL; factor VIII [FVIII] activity, 98 IU/mL).
Further workup with coagulation studies showed decreased factor VIII, vWF antigen, and vWF: ristocetin cofactor
assay, and negative Bethesda assay, indicating acquired von Willebrand disease.
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.
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.
 To rule out coagulopathies, a structured history, Von Willebrand factor assay and ristocetin cofactor
assay may be done if necessary.