The wells of the ELISA strips included in this kit are coated with a monoclonal antibody directed against Von Willebrand Factor: ProPeptide (VWF:PP). The sample is pipetted into a well, followed by a second monoclonal antibody against VWF:PP that is conjugated with an enzyme.

VWF:PP binds to the antibody attached to the solid phase and is immobilised. The second antibody with the conjugated enzyme binds to the immobilised VWF:PP as well. After incubation and washing steps all unbound material is removed and substrate added Is cleaved by the bound enzyme of the conjugate and releases a dye In proportion to the bound VWF:PP. The reaction is stopped after a set time using a stop solution and the absorbance measured. This indicates the concentration of VWF:PP.

The assay is calibrated by parallel measurement of the Included calibrator and its dilutions via a calibration curve. A quality control is possible by simultaneous analysis of the control plasma, which is included in the kit.

The VWF:PP ELISA provides a result with few steps in 90 to 150 min with high precision. The components in the kit for 96 tests have excellent stability. The calibration is performed against the International Standard. Control and calibrator are included in the kit. The VWF:PP is designed for manual processing and automated ELISA systems.

IMPORTANCE OF VWF:PP

Von Willebrand factor (VWF) has several important functions in primary hemostasis. The multimeric protein is found in plasma, platelets and endothelial cells. VWF is also a carrier protein and stabiliser for clotting factor VIII (FVIII) in plasma.

During the biosynthesis of VWF multimers, a 100 kDa glycoprotein propeptide (VWF:PP) is proteolytically cleaved and released into plasma. In certain types of VWF disorders, including inherited or acquired forms, mutations, and some other diseases, abnormal levels of both VWF:PP and VWF:AG (VWF antigen) or VWF activity may be detected, as reflected by the ratio of VWF:PP and VWF:AG.

People with VWF disease show an increased tendency to bleed, e.g. epistaxis, bleeding gums, hematomas or excessive bleeding after dental or other surgical procedures. In extreme cases of absolute deficiency (VWF disease type 3), life-threatening bleeding can occur. In blood, VWF and VWF:PP have very different half-lives (12 versus 2 hours). Measurement of VWF:PP, in addition to VWF:AG, is an important tool of characterising the nature of VWF deficiency, particularly in individuals with a shortened plasma half-life of VWF.

The molar ratio of VWF:PP to VWF can be used as an indicator for the degradation of VWF. An increased ratio of VWF:PP / VWF indicates increased clearance of VWF. These are found in various patients with congenital VWF deficiency, but also in acquired VWF syndrome. An accurate knowledge of the clearance of VWF may influence the choice of therapy, in particular the need to administer VWF concentrates. Increased levels of VWF:PP or an abnormal ratio between VWF:PP and VWF may also be caused by activation of the endothelium or platelets.