Correlation between Two ADAMTS-13 Activity Assays Based on Different Principles.

Defects in ADAMTS-13, the von Willebrand Factor (vWF) cleaving protease, are thought to be the main cause for the microvascular thrombotic disorder TTP (thrombotic thrombocytopenic purpura) that is in more than 90% of cases fatal if not treated early and appropriately. Usually this disease is clinically diagnosed, but in recent years the need for rapid and reliable diagnostic tests for ADAMTS-13 levels has increased. We present here the comparison of two commercially available assays for quantification of ADAMTS-13 activity both suitable for routine analysis but based on different principles. The two assays differ in their test principle and the readout system as follows: Assay 1 is a fluorogenic assay using a FRETS-vWF73 substrate and a kinetic measurement (TECHNOZYM®ADAMTS-13 ELISA); with this assay ADAMTS13 Antigen can also be determined in a second step. Assay 2 is a chromogenic assay and detects the cleaved vWF73 substrate by a specific monoclonal antibody (TECHNOZYM®ADAMTS-13 Activity ELISA). Citrated plasma of normal donors (n=7), of pooled normal plasma (n=15) and of TTP patients (n=14) were tested in both assays. Results are reported in both assays as percentage of normal activity. The standard for both assays is prepared from a pool of 100 normal donors and defined as 100%. The samples comprised a range from 0.2% up to 107% activity. The overall correlation coefficient between the two different activity assays was 0.96. 5 samples were found to have less than 5% activity in both assays. These results show that data obtained by the new TECHNOZYM®ADAMTS-13 Activity ELISA correlate very well with the fluorogenic assay (TECHNOZYM®ADAMTS-13 ELISA) in spite of the fact that these assays are based on very different principles.