Evaluation of a rapid turn-over, fully-automated ADAMTS13 activity assay: a method comparison study

Abstract

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy caused by severely reduced activity of the von-Willebrand factor-cleaving protease ADAMTS13, mainly caused by anti-ADAMTS-13 antibodies. Although several test systems for ADAMTS13 measurement exist, long turn-around times hamper the usability in daily practice. We performed a method comparison study for two commercially available ADAMTS13 assays and evaluated the agreement between the fully-automated rapid turn-over HemosIL AcuStar ADAMTS13 Activity assay and the manually performed TECHNOZYM ADAMTS-13 Activity assay. Twenty-four paired test samples derived from 10 consecutively recruited patients (n = 8, acquired TTP; n = 1, atypical hemolytic uremic syndrome; n = 1, control), of which nine test samples were collected in case of clinically apparent TTP and 13 samples were collected from TTP patients in clinical remission were included. Overall correlation between the TECHNOZYM and AcuStar assay was good with a Pearson R of 0.93 (p < 0.001). Agreement between the assays assessed with the Passing–Bablok analysis showed high agreement with an Intercept of − 2.56 (95% confidence interval [CI], − 5.07 to − 0.86) and Slope of 1.04 (95% CI 0.84–1.17). The absolute mean bias was 2.54% (standard difference [SD], 6.38%; 95% CI to 10.0–15.05%). Intra-method reliability was high with an absolute mean bias of − 0.13% (SD 3.21%; 95% CI to 6.42–6.16%). The observer agreement for categorial thresholds (> or < 10% ADAMTS3 activity) was kappa = 0.82 (95% CI 0.59–1.0). Conclusively, overall agreement between the testing methods was sufficient and we support previously published data suggesting the AcuStar assay being a valuable and accurate tool for ADAMTS13 activity testing and TTP diagnostics.

A multicenter laboratory assessment of a new automated chemiluminescent assay for ADAMTS13 activity

“…We are unsure why our study has uncovered a different pattern of bias between the HemosIL versus Technozym ADAMTS13 Activity assays as reported by Favresse et al, 20 and a higher level of bias to that reported by Valsecchi et al 21 and Stratmann et al 22 Differences may relate to study design and sample selection bias (ie, type of study performed, number and type of test samples assessed). The previous studies were all single‐center studies, and most testing appeared to reflect testing of stored, or retrospective samples, and so some potential for sample selection bias is inevitable.…”

“…There are only three other reports on the HemosIL AcuStar ADAMTS13 Activity assay published in the literature 20‐22 . Favresse et al 20 reported on this assay in a 2018 study that described results of retrospective testing of 38 patient samples (8 TTP patients, 2 patients with moderate ADAMTS13 activity [>10%‐40%] and 28 patients with normal ADAMTS13 activity level [>40%] based on their routine assay [Technozym]).…”

“…A third, more recent publication by Stratmann et al, 22 also compared HemosIL versus Technozym ADAMTS13 Activity assays. They utilized 24 paired test samples derived from 10 consecutively recruited patients (n = 8, acquired TTP; n = 1, atypical hemolytic uremic syndrome; n = 1, control), of which nine test samples were collected in clinically apparent TTP and 13 samples from TTP patients in clinical remission.…”

“…Favresse et al 20 did not identify if testing by HemosIL versus Technozym assays was performed on the same samples on the same day, and may thus have utilized historical data for Technozym. Similarly, Stratmann et al 22 did not identify whether testing was performed on same or different days for each sample and method. In our study, only three sites (sites B, D, and E) performed local testing by Technozym assay, while the remainder only performed HemosIL testing, and referred Technozym testing to another site, including sites B and E. Thus, for most samples, although testing was performed on the same sample, this would have been at different times with most samples.…”

International Council for Standardization in Haematology (ICSH) recommendations for laboratory measurement of ADAMTS13

“…Although there were some discrepancies compared to FRET-VWF73 and a chromogenic activity ELISA, with some samples showing inter-assay disparity at normal and high activity, there was a good correlation between the assays and high agreement in classifying samples with ADAMTS13 levels below 10 IU/ dL. [34][35][36] Due to the reaction principle, these assays are not affected by icterus, lipaemia or plasma turbidity. However, the sample size in two of these studies was small and further evaluations may be needed before their widespread acceptance and regional regulatory bodies may require additional verification or validation procedures.…”