Department of Haematology

Notes

ADAMTS13 (a Distntegrin and Metalloproteinase with a Thrombospondin Type 1 motif, member 13), also known as von Willebrand's Factor-cleaving proteinase (VWFCP), is an enzyme that cleaves the large, multimeric forms of von Willebrand's Factor (vWF). ADAMTS13 deficiency causes an acute haemolytic condition called Thrombotic Thrombocytopenic Purpura (TTP).

In congenital TTP, mutations in the ADAMTS13 gene prevent normal production and/or secretion of the enzyme. In acquired TTP, inhibitory IgG class antibodies interfere with normal ADAMTS13 enzyme activity. In both cases, ultra-large vWF multimers build up in the blood stream. These multimers can bind to the vascular endothelium and circulating platelets triggering platelet aggregation, thrombus formation, and a microangiopathic haemolytic anaemia.

TTP v DIC

It is imperative to correctly distinguish TTP from DIC and the management of the two conditions differs. The coagulation screen will be normal in TTP, whereas in DIC it will be prolonged and the plasma Fibrinogen concentration will be low. Red cell fragmentation may be seen on the blood film in both conditions.

ADAMTS13 Assays

In TTP, both functional and immunological ADAMTS13 assays will show reduced or absent ADAMTS13 enzyme in blood plasma

 

  • Test performed at Oxford Haemophilia Centre

Sample Requirements

2 x 3.0ml or 3.5ml Trisodium Citrate samples are required.

3ml Trisodium citrate



Sample Storage and Retention

  • Pre analysis storage: do not store, send to the laboratory within 2 hours.
  • Sample retention: samples will be retained by Oxford Haemophilia Centre.

As these samples need to be separated and frozen quickly, in most instances it will not be possible to add this request on to a sample previously received by the laboratory.

Reference Ranges

Oxford Haemophilia Centre will report two results:

 

Result Abbreviation Reference Range Units
von Willebrand Protease Activity VWPROT 69 - 144 iu/dl
Protease Inhibitor Activity PRORINH 0 - 13 U/ml

NB: Protease Inhibitor Activity may also be reported as 'positive' or 'negative'.

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