Factor XIa-alpha 1 antitrypsin complex--elevation in the patients with DIC

We developed an assay for the factor XIa-alpha 1 antitrypsin complex (F.XIa-alpha 1AT complex) in plasma. The purified factor XI (F.XI) activated with beta-XIIa and treated with alpha 1 antitrypsin (alpha 1 AT) served as the standard complex. The assay is an enzyme-linked differential antibody immunosorbent assay. The complex level of tested plasma was measured with peroxidase-labeled anti-alpha 1AT Fab' after the addition of 10-fold diluted test plasma (200 microliter) to the anti-F.XI monoclonal antibody beads. To eliminate the effects of plasma, the standard F.XIa-alpha 1AT complex was diluted with F.XI-deficient plasma (10-fold diluted) which did not contain the complex. Purified F.XI (0.08 micrograms/assay, i.e. 100%) was added to the standard F.XIa-alpha 1AT complex, because the absorbance of the standard complex containing F.XI (0.016-0.12 micrograms/assay, i.e. 20-150%) was a little lower than that of the complex alone. The recovery of the F.XIa-alpha 1AT complex added was over 90%. Neither F.XI nor alpha 1AT alone had the color development. The complex level of 25 normal individuals was below the detectable limit (less than 0.18 ng/assay), whereas the 30 patients with disseminated intravascular coagulation (DIC) had a high level complex (0.18-4.2 ng/assay). This assay may be helpful for the diagnosis of DIC.