ADAMTS-13 activity assay

Specimen:

Citrated human plasma. Samples may be stored for up to two hours at temperature or preferably frozen as soon as possible at -20°C. Transport to testing laboratory on dry ice. This test is not widely available – consult laboratory.

Method:

Refer to testing laboratory.

The activity method most commonly used is an ADAMTS-13 activity ELISA.

Reference Interval:

Refer to testing laboratory.

Typical activity assay reference range: 40–130% (guide only).

Application:

The assay determines the level of ADAMTS-13 activity which is usually reduced in the setting of Thrombotic thrombocytopenic purpura (TTP).

Interpretation:

The ADAMTS-13 activity can assist in the diagnosis of TTP. The majority of idiopathic TTP patients demonstrate severely reduced ADAMTS-13 activity (levels of <10%), and demonstration of this supports the diagnosis of TTP. However, a milder reduction in activity may be found in other disease states, and therefore a level of 10-50% should not be used in isolation to establish a diagnosis. ADAMTS-13 levels do not identify all TTP patients who may respond to plasma therapy, and therefore should not be used to direct decisions about initial management.

Specimens for ADAMTS-13 activity should be obtained prior to commencement of plasma transfusion or exchange, as these therapies increase ADAMTS-13 activity. However, therapy should not be delayed while obtaining ADAMTS-13 results and treatment decisions about initiation of therapy should be made on clinical grounds.

Testing for inhibitors of ADAMTS-13 in patients with reduced activity is not yet widely available.

Reference:

George J. How I treat patients with thrombotic thrombocytopenic purpura. Blood 2010; 116: 4060-9.

Scully M, Goodship T. How I treat thrombotic thrombocytopenic purpura and atypical haemolytic uraemic syndrome. Br J Haematol 2014; 164: 759-66.