Platelet Immunology Laboratory

ADAMTS–13 Inhibitor Assay

• Test Code: 3260-02

This is a reflexive test. An inhibition assay will be reported when the protease activity is less than 30%. ADAMTS13 activity is measured by a Fluorescence Resonance Transfer (FRET) Assay in which fluorescence is detected when a synthetic von Willebrand Factor peptide (VWF73) is cleaved by ADAMTS13. Inhibitor activity is determined by measuring the ability of heat treated patient plasma to inhibit ADAMTS13 in normal plasma; inhibitor activity is expressed as percent inhibition of the ADAMTS13.

Strong antibody-mediated inhibition of ADAMTS13 activity (>90%) is seen in approximately half of the patients with acquired TTP. The presence of this level of inhibition strengthens the case for a diagnosis of TTP. The significance of milder ADAMTS13 inhibition is unclear, particularly when the overall ADAMTS13 level is not severely depressed. The assay used does not distinguish between antibody-mediated and non-specific ADAMTS13 inhibition. Caution should be exercised in the interpretation of any assay for ADAMTS13; the results should only be considered in the conjunction with the patient's clinical condition. Previous transfusion, plasma infusion, plasma exchange, or free hemoglobin in the plasma (>2g/L) may affect the level of ADAMTS13 as well as any inhibitors that are present.

• Tests Performed: ADAMTS-13 Activity Assay
• Test Types: Indirect
• Sample required: 5cc citrate (blue top)
• Analytic Time: 2-3 days
  
• Spin and freeze plasma at -20C then ship frozen specimen on dry ice
• Refer to Ordering Information page for submission and transporting requirements