Résumé
Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA), related to a severe functional deficiency of ADAMTS13 activity (<10% of normal). ADAMTS13 activity is thus crucial to confirm the clinical suspicion of TTP, to distinguish it from other TMAs, and to perform the follow-up of TTP patients.
We compared the performance of the commercial chromogenic assay Technozym® ADAMTS13 Activity ELISA (chromogenic VWF73 substrate, Chr-VWF73, Technoclone, Vienna, Austria), to that of our in-house FRETS-VWF73 used as reference method. A large group of 247 subjects (30 healthy volunteers and 217 patients with miscellaneaous TMAs) was studied.
The lower limit of detection of the Chr-VWF73 was 3%, which is well adapted to the clinically relevant threshold for TTP diagnosis (10%). Our results showed a reasonable agreement between FRETS-VWF73 and Chr-VWF73 assays to distinguish samples with an ADAMTS13 activity <10% from those with an ADAMTS13 activity >10%. However, Chr-VWF73 assay provided false negative results in ~12% of acute TTP patients. Inversely, the Chr-VWF73 assay globally underestimated ADAMTS13 activity in detectable values ranging from 11 to 100% (with a great variability compared to FRETS-VWF73), which may be a concern for the follow-up of TTP patients in remission.
In-house assays developed and performed by expert laboratories remain the reference methods that should be used without limitation to control values provided by commercial assays when needed. Also, the development of an international reference preparation will be crucial to improve standardization.
•We compared Chr-VWF73 assay Technozym assay for ADAMTS13 activity to in-house assay•We studied 247 patients with miscellaneous TMAs (French reference center for TMAs)•The LLD of Chr-VWF73 was well adapted for TTP diagnosis•The agreement between both assays to identify values<10% was reasonable•Discrepancies linked to a great variability of measures were frequent in values >10%