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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Von Willebrand Factor Ag

Test Code(s): VWF-AG / XVWFAG

CPT Code(s): 85246

Methodology: Immunoturbidimetry

Request Form: UWHC Special Coagulation Outreach Request Form (UWH SCLR-O)

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: 4 - 7 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 factors 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: 1 mL
Pediatrics: 0.5 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: 1 month at -20C


Reference Interval:

0 days and up:      55-160%

Test Limitations:

The presence of rheumatoid factor leads to an over-estimation of the vWF level.  The extremely rare presence of anti-bovine albumin and/or anti-rabbit antibodies in certain subjects may lead to an over-estimation of the vWF level.

Additional Information:

Individuals of blood group "O" may have lower plasma von Willebrand factor antigen (vWF) levels than those of non-O blood groups. Normal individuals of blood group "O" may have plasma vWF antigen levels as low as 45-55% NPP. The lower limit of the reference interval for individuals of non-O blood groups may be 60-70% NPP. Plasma vWF antigen levels may be increased in acute phase reaction conditions. All vWF antigen results should be interpreted in the context of the clinical setting for each patient.

Von Willebrand Antigen

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