From Denise Jones: Good afternoon George, A colleague of mine recently questioned why we were diluting our anti-Xa
heparins and anti-Xa
LMWHs. We do not dilute Arixtra or rivaroxaban. What
is standard practice for other labs? We use Stago Liquid Anti-Xa reagent and a hybrid curve. Thank you.
Hi, Denise, the specimen dilutions for chromogenic anti-Xa measurement of the various forms of heparin and for the anti-Xa direct oral anticoagulants like rivaroxaban are established by the reagent manufacturer to ensure the analysis occurs within the linear or analytic range. Linearity may differ among reagents and coagulometers and depends upon factor Xa concentration, substrate type and concentration, avidity, and pH. The larger automated coagulometers prepare the specimen dilution automatically, and the manufacturer typically assists the laboratory personnel with the dilutions at the time the assay is validated. Thanks to Stago's Paul Riley, PhD, for assistance with this discussion.