There are some standardization issues related to VWF:CB that MK-8669 clinical trial may limit usefulness and cause confusion. Notably, efficacy of VWF:CB to diagnose and classify of VWD depends on methodology, including collagen used
and coating conditions [24–26]. An automated VWF:CB assay is currently not available. Limited uptake in the USA [21,26] may relate to the fact that there is no FDA approved method. Finally, several commercial and in-house methods have been described and evaluated, but require further standardization . Good quality, accurate laboratory results are essential to facilitate diagnosis in patients with bleeding disorders. However, there is high variability of results reported in different centres, particularly for VWF activity assays. Improvements in accuracy and precision of laboratory assays can be achieved through standardization and external learn more quality assessment (EQA) . An EQA programme was established on behalf of the World Federation of Hemophilia in 1993 . Lyophilized
plasma samples from patients with haemostatic disorders and from normal subjects are distributed to laboratories in both emerging and established heamophilia centres, and the results compared with target values obtained, using the same samples, by up to 900 centres in the United Kingdom National External Quality Assessment Service (UK NEQAS) programme. Problems with diagnostic performance of individual laboratories can be identified, as well as methodological problems associated with specific assays. Interlaboratory variability for VWF activity is particularly MCE公司 marked. Figure 2 shows CVs for assays performed on the same samples by UK NEQAS participants, WFH participants, centres in emerging countries and centres in established countries (primarily International Hemophilia Training Centres). Whilst the precision amongst emerging centres
is comparable with established centres and NEQAS laboratories for screening tests, possibly reflecting their relative simplicity, emerging centres are less able to measure coagulation factors accurately. Troubleshooting and training in the form of regional workshops can help improve laboratory performance by identifying issues, such as calibration problems and poor assay design. A questionnaire in 2007 revealed that 40% of emerging centre laboratories only used a single dilution of test plasma in their assay, an approach previously demonstrated to give inferior results . Furthermore, only 5% of centres used a locally determined reference range. It is interesting to note, however, that performance of emerging centres in the measurement of FVIII and fibrinogen in cryoprecipitate is equivalent to that of established centres (Table 1), which may reflect popular usage of cryoprecipitate for treatment of haemophilia A and VWD in developing countries [30,31].