Normal Reference Values Evaluation of Rapid Chemiluminescent Adamts 13 Activity Assay

ABSTRACT

Introduction: Acquired thrombotic thrombocytopenic purpura (TTP) is a severe, rare, thrombotic microangiopathy (TMA). A diagnosis of acquired TTP is confirmed by a severe deficiency (< 10%) of ADAMTS13 activity. Recently, maybe because of Sars-COV2 Pandemic, in our laboratory we had the impression that normal reference ranges of our ADAMT13 activity assay HemosiL Acustar ADAMTS13 rapid immunoassay, could be larger than manufacturer's. The objective of this study was to evaluate whether manufacturer's are suitable normal reference values for this assay in our laboratory Methods: To evaluate manufacturer's reference limits (60-130.6%) in our laboratory we decided to assay with HemosIL Acustar ADAMTS13 activity test 30 plasma samples from normal subjects. Result(s) 3 out of 20 normal subjects tested showed ADAMTS13 activity outside manufacturer's limits (1 below 60.6% and 2 above 130.6%), therefore even if calculated in a small number of subjects (30 individuals) we decide to try to calculate in house ADAMTS13 reference values. They ranged from 47.5 (10th perc.), 72.5 (25th perc.) and 41.6 (mean- 2sd) to 150.0 (99th perce.), 119,6 (75th perc.) and 152.7 (mean+2sd). To investigate the analytical performance of manufacturer's and calculated cut-offs limits, we re-evaluate one year of ADAMTS13 activity results (95 subjects). ADAMTS13 activity was severely reduced (< 0.7%) in 10 acute TTPs;20 patients with Hemolytic Uremic Syndrome showed ADAMTS13 activity above manufacturer's and in all calculated cut-offs;21/45 patients with TTPs in remission phase showed ADAMTS activity below all in house calculated cut off and 24/45 showed ADAMTS activity below manufacturer's;12/20 other patients showed ADAMTS activity below all in house calculated and manufacturer's cut offs, all of them were Sars COV2 positive subjects Conclusion(s) In conclusion HemosiL Acustar ADAMTS13 activity calculated cut-offs in our laboratory were larger than manufacturer's reference range. By the analysis of one year ADAMTS13 activity dosages both manufacturer's and calculated cut-offs showed similar performances but our calculated reference ranges even if obtained by the analysis of a small number of normal subjects were found to be more similar to literature ELISA (40-130%) and FRET (45-147%) ADAMTS13 activity normal values.