ADAMTS13 Assay

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 University Hospitals Bristol NHS Foundation Trust (Bristol Royal Infirmary)
• Seek advice from Consultant Haematologist prior to taking any samples

Sample Requirements

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

Form for Completion

Complete the attached form, as much as possible and send to the Haematology department along with the citrate samples. Link to form.

Turnaround Times

• Known Haematology patients / monitoring – Tested within 7 days of receipt of samples at Bristol, with the exception of Public and Bank holidays. One batch is normally tested per week depending on clinical needs.
• Urgent requests: Tested within 24 hrs from when sample received in laboratory at Bristol. Samples must be in the laboratory by 12 noon if urgent and require testing on the same day.

Sample Storage and Retention

• Pre analysis storage: do not store, send to the laboratory immediately.
• Sample retention: samples will be retained by Bristol.

It will not be possible to add this request on to a sample previously received by the laboratory.

Reference Ranges

Bristol Royal Infirmary will report two results:

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