Rodeghiero F, Castaman G
Divisione di Ematologia, Ospedale San Bortolo, Vicenza.
Ric Clin Lab. 1990 Apr-Jun;20(2):143-53. doi: 10.1007/BF02877561.
Von Willebrand factor (vWf) is a multimeric and multivalent adhesive protein which is essential for platelet adhesion to subendothelium and for stabilization of factor VIII procoagulant activity in circulation. The quantitative measurement of vWf involves essentially two different approaches. The first is based on the interaction between vWf and Gp Ib of the platelet membrane in presence of ristocetin (ristocetin cofactor activity, RiCof) and depends not only on the amount of the factor but also on its ability to bring about this interaction, large multimers being more active. The second approach involves the immunological quantitation of vWf (vWf:Ag) by its interaction with specific polyclonal or monoclonal antibodies as measured by several methods, i.e., electroimmunoassay, immunoradiometric assay and immunoenzymatic assay. Although in the majority of type II von Willebrand disease (vWd) with dysfunctional vWf there is a discrepancy between RiCof and vWf:Ag, it should be emphasized that RiCof activity does not entirely reflect the 'true' activity of vWf since it does not explore all the functions of this factor; furthermore, the relationship between degree of multimerization and RiCof level is not always tenable, as for example in vWd 'Vicenza'. For the diagnosis of congenital and acquired vWd RiCof assay together with family investigation is the eligible test, with an estimated ability to detect at least 50% of the carriers of the abnormal gene, including mildly affected patients; vWf:Ag appears less sensitive and, on the basis of studies carried out in our laboratory, a relative sensitivity of 64% is proposed. Both assays require the definition of separate normal ranges for children and adults and for 0 and non-0 blood group subjects; a nonparametric approach in a large sample of normal subjects is advisable. With RiCof assay performed by an aggregometric method using formalin-fixed platelets an interassay variability of 6% and 8.5% respectively for high- and low-control plasma was found in our laboratory. With vWf:Ag assayed by an ELISA method a variability of 7% for low- and 6% for high-control plasma was found. Thus, both methods appear sufficiently precise for clinical use. The use of an internal pool calibrated against an international standard allows to perform comparable interlaboratory measurements. To further improve standardization of these assays, collaborative studies seem urgently required.
血管性血友病因子（vWf）是一种多聚体和多价黏附蛋白，对于血小板黏附于内皮下以及循环中凝血因子Ⅷ促凝活性的稳定至关重要。vWf的定量检测主要涉及两种不同方法。第一种基于在瑞斯托霉素存在的情况下vWf与血小板膜糖蛋白Ib之间的相互作用（瑞斯托霉素辅因子活性，RiCof），它不仅取决于该因子的量，还取决于其引发这种相互作用的能力，大分子多聚体更具活性。第二种方法涉及通过几种方法（即电免疫测定、免疫放射测定和免疫酶测定）测量vWf与特异性多克隆或单克隆抗体的相互作用来对vWf进行免疫定量（vWf:Ag）。尽管在大多数具有功能异常vWf的Ⅱ型血管性血友病（vWd）中，RiCof与vWf:Ag之间存在差异，但应强调的是，RiCof活性并不完全反映vWf的“真实”活性，因为它并未探究该因子的所有功能；此外，多聚化程度与RiCof水平之间的关系并不总是成立，例如在“维琴察”型vWd中。对于先天性和获得性vWd的诊断，RiCof检测结合家族调查是合适的检测方法，估计能够检测出至少50%的异常基因携带者，包括症状较轻的患者；vWf:Ag似乎不太敏感，根据我们实验室开展的研究，其相对敏感性为64%。两种检测都需要为儿童和成人以及O型和非O型血型受试者分别定义正常范围；在大量正常受试者中采用非参数方法是可取的。在我们实验室中，使用福尔马林固定血小板通过凝集法进行RiCof检测时，高对照血浆和低对照血浆的批间变异分别为6%和8.5%。采用ELISA法检测vWf:Ag时，低对照血浆的变异为7%，高对照血浆的变异为6%。因此，两种方法对于临床应用而言似乎都足够精确。使用根据国际标准校准的内部混合样本可进行具有可比性的实验室间测量。为了进一步提高这些检测的标准化程度，迫切需要开展协作研究。
