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| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # |
von Willebrand Factor GPIbM Activity
Test Code13995
Preferred Specimen
Collection Instructions:
Platelet-poor plasma: Centrifuge light blue-top tube for 15
minutes at approximately 1500 g within 60 minutes of
collection. Using a plastic pipette, remove plasma, taking
care to avoid the WBC/platelet buffy layer and place into
a plastic vial. Centrifuge a second time and transfer
platelet-poor plasma into a new plastic vial. Plasma must
be free of platelets (<10,000/uL). Freeze immediately and
ship on dry ice. Alternative methods for preparation of
platelet poor plasma may be used if validated by the
laboratory.
Note: storage of whole blood at refrigerated temperatures
prior to processing may lead to cryoprecipitate formation
and falsely low Factor VIII and von Willebrand Factor
studies.
PREFERRED
1 mL frozen platelet-poor plasma (LB, light blue-top tube,
3.2% citrate), frozen
Minimum: 0.5 mL
RT: Unacceptable
Refrigerated (cold packs): Unacceptable
Frozen: 90 days
Platelet-poor plasma: Centrifuge light blue-top tube for 15
minutes at approximately 1500 g within 60 minutes of
collection. Using a plastic pipette, remove plasma, taking
care to avoid the WBC/platelet buffy layer and place into
a plastic vial. Centrifuge a second time and transfer
platelet-poor plasma into a new plastic vial. Plasma must
be free of platelets (<10,000/uL). Freeze immediately and
ship on dry ice. Alternative methods for preparation of
platelet poor plasma may be used if validated by the
laboratory.
Note: storage of whole blood at refrigerated temperatures
prior to processing may lead to cryoprecipitate formation
and falsely low Factor VIII and von Willebrand Factor
studies.
PREFERRED
1 mL frozen platelet-poor plasma (LB, light blue-top tube,
3.2% citrate), frozen
Minimum: 0.5 mL
RT: Unacceptable
Refrigerated (cold packs): Unacceptable
Frozen: 90 days
Minimum Volume
0.5 mL
Transport Container
Light Blue 3.2% Sodium Citrate
Transport Temperature
Frozen
Specimen Stability
Room Temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 3 months (-20c)
Refrigerated: Unacceptable
Frozen: 3 months (-20c)
Methodology
Latex-based turbidimetric
Setup Schedule
Tuesday, Thursday, Saturday All Shifts
Report available: 3 Days
Report available: 3 Days
Reference Range
43-207 %
Clinical Significance
von Willebrand disease (VWD) is the most frequent
inherited bleeding disorder and is characterized by
either a quantitative or qualitative defect of von
Willebrand Factor (VWF). During primary hemostasis, VWF
mediates platelet adhesion and aggregation via binding to
the platelet glycoprotein Ib (GPIB) receptor at the site
of injury. VWF is also the specific carrier protein of
Factor VIII, protecting FVIII from proteolytic
degradation in circulation. The initial screening
evaluation of VWD includes testing for VWF antigen, VWF
activity, and Factor VIII activity. Historically, the
most commonly performed VWF activity assay has been the
Ristocetin Cofactor assay (VWF:RCo). The GPIbM activity
assay is a ristocetin independent activity assay and
provides several advantages over the VWF:RCo assay -
improved sensitivity (e.g. lower reporting limit) and
precision, and insensitivity to benign VWF variants (seen
in 60-70% and 15-20% of African and Caucasian descent,
respectively) that reduce ristocetin interaction and
potentially leading to a potentially false diagnosis of
VWD or type 2 VWD (VWD associated with markedly decreased
VWF activity compared to VWF antigen level). It should be
noted that reference intervals are from non-ABO typed
donors.
inherited bleeding disorder and is characterized by
either a quantitative or qualitative defect of von
Willebrand Factor (VWF). During primary hemostasis, VWF
mediates platelet adhesion and aggregation via binding to
the platelet glycoprotein Ib (GPIB) receptor at the site
of injury. VWF is also the specific carrier protein of
Factor VIII, protecting FVIII from proteolytic
degradation in circulation. The initial screening
evaluation of VWD includes testing for VWF antigen, VWF
activity, and Factor VIII activity. Historically, the
most commonly performed VWF activity assay has been the
Ristocetin Cofactor assay (VWF:RCo). The GPIbM activity
assay is a ristocetin independent activity assay and
provides several advantages over the VWF:RCo assay -
improved sensitivity (e.g. lower reporting limit) and
precision, and insensitivity to benign VWF variants (seen
in 60-70% and 15-20% of African and Caucasian descent,
respectively) that reduce ristocetin interaction and
potentially leading to a potentially false diagnosis of
VWD or type 2 VWD (VWD associated with markedly decreased
VWF activity compared to VWF antigen level). It should be
noted that reference intervals are from non-ABO typed
donors.
