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Useful For
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Measurement of VWF activity as a part of the diagnosis of VWD and its classification .Also in the differentiation of VWD from Hemophilia A.
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Method name and description
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Latex (Immunogenic)
Test is performed using Sysmex CS5100 analyzer. The assay principle makes use of the binding of VWF to its receptor Glycoprotein Ib (GPIb). (GP Ib) is the main VWF receptor on platelets. Polystyrene particles are coated with an antibody against (GPIb). Recombinant GPIb (two gain-of-function mutations included) is added and binds to the antibody as well as to the VWF of the sample. Due to the gain-of –function mutations, VWF binding to GPIb does not require ristocetin. This VWF binding induce a particle agglutination which can be measured as increase in extinction by turbidimetric measurements.
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Reporting name
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Von Willebrand Factor Activity(VWF Ac)
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Clinical information
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Von Willebrand factor (VWF) is synthesized by the endothelial cell and megakaryocyte and is present in these cells, as well as in platelets, subendothelial tissue, and plasma. VWF is a multimeric, high-molecular glycoprotein involved in primary hemostasis, supporting platelet adhesion and aggregation via binding to the platelet glycoprotein Ib (GPIb) receptor under shear stress at the site of injury. Furthermore, VWF is the specific carrier protein of FVIII, protecting FVIII against inactivation and rapid clearance.
Von Willebrand Disease (VWD) is the most frequent congenital human bleeding disorder and is caused by a reduction or dysfunction of von Willebrand Factor (VWF).
VWD is an autosomal inherited disorder of three different types: type 1 (partial quantitative deficiency of VWF), type 2 (qualitative VWF defects) and type 3 (almost complete deficiency of VWF). VWD type 2 can be further sub-typed into 2A, 2B, and 2M based on their different multimeric pattern and/or altered platelet affinity. Type 2N is characterized by a reduced FVIII binding activity with otherwise normal functionality. These variants are differentiated on the basis of a series of laboratory tests for VWF activity, VWF antigen, platelet function testing (PFA Systems), FVIII activity, platelet count, and VWF multimer analysis. Von Willebrand Disease can also occur as an acquired bleeding disorder. Bleeding symptoms in all types of VWD are primarily mucosal, including epistaxis, menorrhagia, gastrointestinal bleeding, and ease of bruising, but surgical or posttraumatic bleeding can also occur.
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Specimen type / Specimen volume / Specimen container
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Plasma Na Cit. Platelet-poor plasma.
Specimen Volume: 2.7 ml.
Container/Tube: Light-blue top (citrate)
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Collection instructions / Special Precautions / Timing of collection
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- Samples collected in HMC facilities MUST reach the coagulation laboratory within 1 hour of collection.
- Samples collected in non-HMC facilities / external clients: MUST reach coagulation laboratory within 1 hour of collection, if not applicable, centrifuge the whole blood and carefully remove the plasma (by pipette not by decanting) and send it in a temperature-controlled environment (18- 25 ºC) within 2 hours of centrifugation. If the transportation of the plasma can’t be within a maximum of 2 hours, prepare platelet-poor plasma as follows:
- Re-centrifuge the plasma again.
- Remove the top portion of plasma leaving approximately 250 ul in the bottom to discard.
- The double-centrifuged plasma should be aliquoted into labeled plastic tubes.
- Freeze immediately at -20 ºC or below
- Specimens must arrive frozen.
- If patient HCT is >55%, test will not be processed. The ordering Physician will be contacted to reorder the test and call the patient to go to Phlebotomy for recollection. Instruct the patient to inform the phlebotomy about his high HCT% , the phlebotomy will contact the lab to request a coagulation tube after adjusting amount of anticoagulant.
Note:
Collection of blood for coagulation testing through intravenous lines that have been previously flushed with heparin should be avoided, if possible. If the blood must be drawn through an indwelling catheter, possible heparin contamination and specimen dilution must be considered. When obtaining specimens from indwelling lines that may contain heparin, the line should be flushed with 5 mL of saline, and the first 5 mL of blood or 6-times the line volume (dead space volume of the catheter) be drawn off and not used for coagulation testing. For those specimens collected from a normal saline lock (capped off venous port) twice the dead space volume of the catheter and extension set should be discarded.
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Relevant clinical information to be provided
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Patient's blood group O and Non O. Patient/family history of bleeding disorder. History of anticoagulant therapy. History of chronic diseases
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Storage and transport instructions
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Specimen Rejection Criteria
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Specimens with no label or missing required identification
Broken, leaking or contaminated specimen
Clotted samples
Under-filled or overfilled sample tubes.
Wrong sample container sample received
Improper specimen transport temperature (e.g. like specimens which are needed to be sent on ice)
Old specimen (test-dependent)
Grossly Hemolyzed sample (test-dependent)
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Biological reference intervals and clinical decision values
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Reference ranges:
Blood group O: 43.6-140.5%
Blood group Non-O: 63.3 – 199.7%
Normal, full term born infants may have mildly increased levels which reach adult levels by 90 days. Healthy, premature infants (30-36 weeks gestation) may have increased levels that reach adult levels by 180 days.
Individuals of blood group O may have lower plasma VWF activity than those of other ABO blood groups, such that apparently normal individuals of blood group O may have plasma VWF activity as low as 40% to 50%, whereas the lower limit of the reference range for individuals of other blood groups may be 60% to 70%.
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Factors affecting test performance and result interpretation
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No interference up to:
Triglycerides 889 mg/dL
Hemoglobin 1000 mg/dL
Bilirubin 60 mgl/dL
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Turnaround time / Days and times test performed / Specimen retention time
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For routine ordered test : 3 working days
For stat ordered test :
- During the Laboratory working hours from 0700 hours to 1500 hours (Sunday to Thursday): TAT is Within 8hrs.
- After duty hours, weekends and on holidays: TAT is within 12 hrs. with the following requirements:
- Laboratory should be notified by telephone about the sending of a STAT sample.
- The sample should be hand-delivered to the central processing area and requesting them to deliver it immediately to the hematology coagulation lab.
Test is done : Daily.
Specimen retention time: NA
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