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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Von Willebrand Factor Activity

Test Code(s): VWFACT / HCVWFACT

CPT Code(s): 85245

Methodology: Immunoassay

Clinical Significance: The von Willebrand Factor Activity reflects the binding of a monoclonal antibody to a confirmation epitope of the von Willebrand antigen.

Days Performed: Mon-Fri, dayshift - day varies. Specimens are accepted at any time. Testing required during off hours must be approved by a Coagulation physician. Call 263-5005 before collection.

Turnaround Time: Stat: 1 working day.
Routine: 7 - 10 working days.


Specimen Requirements

Specimen: Blood

Collection Instructions: Do NOT draw through a line containing heparin.  The venipuncture MUST be atraumatic to avoid hemolysis and contamination with tissue factor and platelets. Tube must be allowed to fill completely.  

Collection Container: Preferred: Light blue top (3.2% NaCitrate)

Collection Volume: Preferred: Full 3.5 mL tube
Pediatrics: Pediatric tube filled to fill mark

Sample Analyzed: Plasma

Volume Required: Preferred: 2 mL
Pediatrics: 1 mL

Specimen Processing: Centrifuge specimen to yield platelet poor plasma (platelet count should be less than 10 K/uL). Separate plasma and transfer to plastic tube or vial. Freeze plasma within 4 hours of collection at -20C or below.

Specimen Transport: Transport whole blood specimen at room temperature to UWHC Core Laboratory (B4/220) within 4 hours of collection. See Specimen Processing for instructions if transport criteria are not met. Transport frozen plasma aliquot on dry ice to UWHC Core Laboratory (B4/220).

Unacceptable Criteria: Hemolyzed specimens, clotted specimens, partially filled tubes and whole blood specimens greater than 4 hours old when received by the laboratory are not acceptable.

Stability: Ambient: 4 hours on spun tube
Refrigerated: Not acceptable
Frozen: 2 weeks at -20C; 6 months at -70C


Interpretation

Reference Interval:

0 days and up:         50-170%

Test Limitations:

The presence of rheumatoid factor, anti-bovine antibodies and/or anti-rabbit antibodies may produce an overestimation of the test result.

Additional Information:

Individuals of blood group "O" may have lower plasma von Willebrand factor activity levels than those of non-O blood groups.  Normal individuals of blood group "O" may have plasma vWF activity levels as low as 40-50% NPP.  The lower limit of the reference interval for individuals of non-O blood groups may be 60-70% NPP.  All vWF activity results should be interpreted in the context of the clinical setting for each patient. 

Ristocetin Cofactor Activity

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