vWF: Ac (von Willebrand Factor activity) (Citrated plasma, frozen (cp))

The von Willebrand's syndrome (vWS) is the most common cause of a congenital bleeding tendency (mild form up to 2 % of the population).

The von Willebrand's syndrome can also be drug-induced (frequently valproate-induced) or acquired, e.g. by autoantibodies and with lymphoproliferative diseases.

The syndrome is usually not detected by means of common global tests such as Quick value, PTT or thrombin time. Often, however, the bleeding time is prolonged.

vWS can be classified into different types which require different therapeutic consequences. With positive basic diagnostics, special methods are available for differentiation (multimeric analysis, molecular genetic methods).

Classification of the hereditary vW syndrome:

• Type 1: Partial quantitative deficiency of vWF

  Frequency approx. 70 - 80 %, autosomal dominant inheritance

• Type 2: Qualitative defect/deficiency in vWF Frequency approx. 15 - 20 %, autosomal dominant or recessive inheritance

  Type 2 differentiates between 4 different subtypes which can usually be differentiated by means of the multimeric analysis. The most important subtype of these is type 2A.

• Type 3: Virtually complete quantitative deficiency of vWF: Total absence of vWF (at most traces of vWF:Ag detectable), thus half-life period of factor VIII reduced to 1 hour. The haemophilia-like bleeding type predominates in the end even though the platelet function is also strongly impaired.

Types 1 to 3 can be differentiated by the above-mentioned ratio formation:

• A vWF:Ac/vWf:Ag ratio below 0.6 indicates a type 2.
• With purely quantitative reductions, i.e. type 1 and type 3, the concentrations of vWF:Ag, factor VIII and vWF:Ac are equally reduced, so the ratio is usually normal.

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