PB0301 - Multi-centre performance evaluation of ADAMTS13 activity quantification using three different measurement technologies

Background: ADAMTS13 activity (ADAMTS13:Ac) measurement is an important diagnostic marker of acute thrombotic thrombocytopenic purpura (TTP), defined as levels < 10%. As delay to, or incorrect treatment in TTP is detrimental, testing is often urgent. Increasing numbers of commercial assays are available for diagnostic purposes using differing technology. Enzyme linked immunosorbent assay’s (ELISA) are frequently used, but are laborious, with turnaround times of 3-4hrs. Rapid ADAMTS13:Ac assays with ~30min turnaround time are now commercially available and warrant evaluation.

Aims: Method comparison of two rapid ADAMTS13:Ac assays against current ELISA methodology at three regional TTP centres (UK).

Methods: Method comparison performed using 110 samples from patients with clinical suspicion of TTP or undergoing TTP treatment. Samples were tested using rapid Technofluor fluorescence resonance energy transfer (FRET) (Technoclone) and HemosIL AcuStar chemiluminescent immunoassay (CIA) (Werfen) assays, according to manufacturer’s instructions. Results were compared to the Technozym ELISA assay (Technoclone). An estimation of bias was obtained by Bland Altman analysis.

Results: ADAMTS13:Ac analysis by FRET displayed a positive bias strengthening with rising values in comparison to ELISA. Method comparison by Bland Altman’s analysis highlighted a mean difference of 10.2% between FRET and ELISA. The CIA showed a mean difference of -2.3% from ELISA (Figure 1).
17 results were consistent with a diagnosis of TTP ( < 10%) by all methods. 7 results were < 10% by two methods, and 2 were < 10% by CIA only.

Conclusion(s): Real-world patient testing demonstrates significant variability between ADAMTS13:Ac methods, impacting TTP diagnosis, follow up and treatment decisions. Although good concordance was seen at levels of < 10% across all methods, increased variability was observed for levels of 10-50%. At these levels increased patient monitoring and subsequent treatment may be indicated to avoid frank relapse. ADAMTS13:Ac results should be obtained from consistent methodology, and where cross-site patient management occurs variation should be estimated.