Performance Evaluation of the New Screening Assay for ADAMTS-13 Activity

Background: The standard laboratory test for ADAMTS-13 Activity is an ELISA, which requires at least 4 h to process. It tends to be performed by specialized laboratories only. Therefore, for a physician to receive a patient's ADAMTS-13 activity result can range from 24 h to as much as one week. This delay in reporting could have a negative impact on patient care. With the new TECHNOSCREEN® ADAMTS-13 assay, a rapid and simple assay is available and allows the physician to have an initial reportable result for ADAMTS-13 Activity within 1 hour from the blood draw. Aim of this study was to evaluate the assay performance in regards of specificity and sensitivity.

Methods: The assay is based on flow through technology, which allows for simple, rapid processing. Plasma samples are pre-incubated with a substrate which is cleaved by ADAMTS-13 present in the plasma. This pre-treated sample is applied to the test unit which contains a membrane with immobilized antibodies specific for the cleaved substrate. As the sample flows through the membrane into an absorbent pad the cleaved substrate binds to capture antibody. A secondary antibody is used to detect the membrane bound complex. Using a gold conjugate a red colour is produced. The colour intensity is proportional to the level of ADAMTS-13 activity in the plasma sample and compared with a colour standard card, allowing semi-quantitative analysis of the patient sample. The assay can be performed at room temperature without specialized laboratory equipment. The assay processing time is under 30 minutes. The test is designed for evaluation of a single patient sample, with a positive control run in parallel. For the present performance evaluation 77 patient sampleswere determined in the screening assay. As reference method, the ADAMTS-13 activity level was determined for all patient samples with the TECHNOZYM® ADAMTS-13 activity ELISA.

Results: The designed assay cut-off value of 10% ADAMTS-13 Activity is clinically relevant for differentiation of TTP patients. The PPV (positive predictive value) was at 95% whereas the NPV (negative predictive value) was 91% using the screening assay when compared to the gold standard ELISA.The sensitivity and specificity were 93% and 94% respectively.

Conclusion: TECHNOSCREEN® ADAMTS-13 as a rapid and simple assay is versatile and suitable as a cost effective screening assay enabling quick turnaround for ADAMTS-13 activity based diagnostics.

No conflict of interest has been declared by the author(s).