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Collagen-binding Activity (CBA) Profile
- vWF Collagen Binding Activity
Collagen-binding ratio; vWF antigen; vWF collagen-binding activity
Screen for the presence of type II von Willebrand disease in plasma6
vWF is an acute phase reactant protein and levels may be increased transiently into the normal range in some individuals with mild vWD following adrenergic stimulation or in response to certain drug therapies such as DDAVP or estrogen.
This procedure may be considered by Medicare and other carriers as investigational and, therefore, may not be payable as a covered benefit for patients.
Enzyme-linked immunosorbent assay (ELISA)
• CBA activity: 50% to 150%
• CBA ratio: 0.6−5.0
• vWF antigen: 50% to 150%
The collagen binding assay (CBA) can aid in the differentiation between von Willebrand disease type I and type II when used in conjunction with the vWF antigen assay. This assay evaluates the ability of high molecular weight multimers present in the patient's sample to bind collagen which is coated on the microtiter plates. The amount of vWF bound is measured using peroxidase-conjugated antibodies to human vWF. Following the addition of substrate, color intensity is proportional to the high molecular weight multimers present in the sample. Results are expressed as percent collagen-binding activity and also as a ratio of percent collagen-binding activity to total vWF antigen. The CBA activity correlates more closely with vWF function and bleeding problems than ELISA for vWF antigen levels.
Citrated plasma samples should be collected by double centrifugation. Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples except when using a winged blood collection device (ie, "butterfly"), in which case a discard tube should be used.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. Centrifuge for 10 minutes and carefully remove 2/3 of the plasma using a plastic transfer pipette, being careful not to disturb the cells. Deliver to a plastic transport tube, cap, and recentrifuge for 10 minutes. Use a second plastic pipette to remove the plasma, staying clear of the platelets at the bottom of the tube. Transfer the plasma into a LabCorp PP transpak frozen purple tube with screw cap (LabCorp N° 49482). Freeze immediately and maintain frozen until tested. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.
Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.
Freeze; four freeze/thaw cycles are acceptable. Stable refrigerated for four hours.
Causes for Rejection
Lipemia; icteric specimen; hemolysis; clotted specimen; specimen contaminated with heparin (ie, drawn with blood gases)