Molecular testing to confirm a phenotypic diagnosis of von Willebrand disease type 2B and to distinguish from pseudo (platelet-type) vWD.
- Patient Preparation
- Lavender (EDTA), pink (K2EDTA) or yellow (ACD Solution A or B).
- Specimen Preparation
- Transport 3 mL whole blood. (Min: 1 mL)
- Storage/Transport Temperature
- Unacceptable Conditions
- Ambient: 72 hours; Refrigerated: 1 week; Frozen: Unacceptable
Characteristics: Mucocutaneous bleeding after brushing or flossing teeth, unexplained bruising, prolonged repeated nosebleeds, menorrhagia, and prolonged bleeding following childbirth, trauma or surgery.
Incidence: Approximately 1 in 100 to 1 in 1000 individuals.
Inheritance: Autosomal dominant for types 2B, 2M and most of 2A; autosomal recessive for 20 percent of 2A.
Penetrance: Dominant mutations are incompletely penetrant when VWF:Ag and VWF:RCo levels are 25-50 IU/dL. Full penetrance is expected when VWF:Ag and VWF:RCo levels are less than 25 IU/dL.
Cause: Pathogenic VWF mutations in exon 28.
Clinical Sensitivity: 80 percent for vWD types 2A, 2B, and 2M; unknown for other vWD subtypes.
Methodology: Bidirectional sequencing of VWF exon 28 and its intron-exon boundaries.
Analytical Sensitivity and Specificity: 99 percent.
Limitations: Diagnostic errors can occur due to rare sequence variations. Regulatory region mutations, deep intronic mutations, and large deletion/duplications will not be detected. Mutations lying outside of VWF exon 28 are not evaluated.
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
|Component Test Code*||Component Chart Name||LOINC|
|2005487||vWD2B (VWF) Specimen|
|2005488||vWD Type 2B (VWF) Sequencing Interp|
- VWD type 2B sequencing assay
- VWF2B Sequencing