OC 15.4 - ADAMTS13 results for the SSC Plasma Standard from ECAT and UK NEQAS External Quality Assessment Programmes

Background: ADAMTS13 plays an important role is the size regulation of von Willebrand factor. ADAMTS13 plays an important role in the diagnosis of thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) by activity and antigen assays. The SSC/ISTH Secondary Coagulation Standard is available to manufacturers of coagulation diagnostic reagents. Up to now this standard has not been calibrated for ADAMTS13. Calibration of SSC plasma standard for ADAMTS 13 would facilitate hamonisation of calibration and use of IU.

Aims: To assess ADAMTS13 activity and antigen for the SSC/ISTH Secondary Coagulation Standard using data from two external quality assessment (EQA) organisations.

Methods: Both the ECAT Foundation (The Netherlands) and UKNEQAS Blood Coagulation (United Kingdom) have distributed the SSC plasma standard (lot #5) as a ‘blinded’ sample to participants for ADAMTS13 activity and antigen testing. Data were collected by each provider, anonymised, and pooled. Results were analysed for each of the EQA providers, and by assay principle and method-specific comparisons and pooled together. Median results, range and coefficient of variation were determined. Statistical analyses were performed using the Student’s T test, Wilcoxon-Mann-Whitney Test and ANOVA.

Results: Data of 178 participants were included. Table 1 shows a summary of the results for both ADAMTS13 activity and antigen. The overall median activity is 84 IU/dL and for antigen 68.5 IU/dL.
There were no significant differences between results of the two EQA providers. For ADAMTS13 activity the Fluorescence Resonance Energy Transfer (FRET) assay, mainly homemade assays, demonstrates significantly higher results in comparison to Enzyme ImmunoAssays (p=0.046) and Chemiluminescence Latex Immunoassay (CLIA) / Fluorescence Immunoassay (FIA) (p=0.031).
For antigen no significant difference between the two methods was observed.

Conclusion(s): For the first time, values for ADAMTS13 activity (84 IU/dL) and antigen (68.5 IU/dL) have been determined for the SSC secondary coagulation standard, with excellent agreement between 2 different EQA programmes.