Rox Factor XIa is a chromogenic assay kit based upon FXa generation for quantitative activity determination of Factor XIa in enriched or highly purified protein preparations. Not intended for analysis of plasma.

  • Detection Limit = about 0.03 mU/mL
  • No use of human plasma

Rossix Rox Factor XIa chromogenic assay kit

Human FXIa is determined from its activation of human Factor IX and ensuing activation of human Factor X. Generated Factor Xa is then measured with a chromogenic FXa substrate.

The activation of Factor IX is performed in two steps:

  1. Initial activation of FIX in the absence of phospholipids.
  2. Continued activation of FIX in the presence of FX and phospholipids, therewith allowing concomitant activation of FX.

Rossix Rox Factor XIa chromogenic assay kit measurement principle



Factor XI (FXI) has been identified as a risk factor for both arterial and venous thromboembolism (Ref 1-3). Plasma fractionation procedures may sometimes be associated with inadvertent activation of hemostasis zymogen proteins such as FXI and Factor XIa (FXIa) can be a contaminant in intermediate or final products such as immunoglobulins (IgG). Thromboembolic events have been reported to occur after intravenous administration of IgG and ensuing detailed analyses appeared to link these events to the presence of FXIa in the administered IgG batches (4-7). Routine tests such as the NAPTT may not be sufficiently sensitive to detect relevant low levels of FXIa, possibly partly explained by matrix interference. Rox Factor XIa offers a highly sensitive chromogenic method for determination of sub-picomolar levels of FXIa, therewith allowing high sample dilutions and minimizing interference from the sample matrix and from contaminating proteins such as kallikrein, zymogen FXI and FIXa. Read more…

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