Nichols, William L.

IntroductionHaemostatic assessments of patients with von Willebrand disease (VWD) who undergo total knee arthroplasty (TKA) and total hip arthroplasty (THA) have mainly relied on subjective parameters.AimsTo compare objective haemostatic outcomes of TKA/THA in VWD patients and controls without bleeding disorders.MethodsWe retrospectively analysed haemostatic outcomes in VWD patients undergoing TKA/THA from 1993 to 2011 and compared them with two matched controls per operation. Using one‐way analysis of variance, we tested the effect of VWD on bleeding risk after TKA and THA.ResultsTwelve VWD patients (6 type 1, 3 type 2M, 1 each of types 2A/2B/3) undergoing 19 operations (12 TKA, 7 THA) were matched to 38 controls. One (5%) of 19 operations in VWD patients and none of the control operations met clinical criteria for major bleeding. Baseline and postoperative day 1 haemoglobin levels, postoperative blood loss, transfused red blood cells (RBCs) and mean hospitalization days were not significantly different. More VWD patients than controls received RBC transfusions [12 (63%) vs. 12 (32%)]. Only 9 (47%) VWD patients vs. 38 (100%) controls received pharmacologic VTE prophylaxis. No postoperative symptomatic VTE occurred in either group.ConclusionIn this largest, single‐institutional study, von Willebrand factor replacement based on daily levels resulted in low frequency of major bleeding in VWD patients after TKA/THA. RBC transfusion was more frequent compared with matched controls, but other objective measures of haemostasis were similar. Lack of sufficient details in published reports precluded comparison of haemostatic outcomes.

BackgroundThe ability of von Willebrand factor (VWF) to bind platelet GP Ib and promote platelet plug formation is measured in vitro using the ristocetin cofactor (VWF:RCo) assay. Automated assay systems make testing more accessible for diagnosis, but do not necessarily improve sensitivity and accuracy.ObjectiveWe assessed the performance of a modified automated VWF:RCo assay protocol for the Behring Coagulation System (BCS®) compared to other available assay methods.MethodsResults from different VWF:RCo assays in a number of specialized commercial and research testing laboratories were compared using plasma samples with varying VWF:RCo activities (0–1.2 IU mL−1). Samples were prepared by mixing VWF concentrate or plasma standard into VWF‐depleted plasma. Commercially available lyophilized standard human plasma was also studied. Emphasis was put on the low measuring range. VWF:RCo accuracy was calculated based on the expected values, whereas precision was obtained from repeated measurements.ResultsIn the physiological concentration range, most of the automated tests resulted in acceptable accuracy, with varying reproducibility dependent on the method. However, several assays were inaccurate in the low measuring range. Only the modified BCS protocol showed acceptable accuracy over the entire measuring range with improved reproducibility.ConclusionsA modified BCS® VWF:RCo method can improve sensitivity and thus enhances the measuring range. Furthermore, the modified BCS® assay displayed good precision. This study indicates that the specific modifications − namely the combination of increased ristocetin concentration, reduced platelet content, VWF‐depleted plasma as on‐board diluent and a two‐curve calculation mode − reduces the issues seen with current VWF:RCo activity assays.