Summary
Rivaroxaban is an oral, direct factor Xa inhibitor. Routine coagulation monitoring
is not required, but a quantitative determination of rivaroxaban concentrations might
be useful in some clinical circumstances. This multicentre study assessed the suitability
of the anti-factor Xa chromogenic assay for the measurement of rivaroxaban plasma
concentrations (ng/ml) using rivaroxaban calibrators and controls, and the inter-laboratory
precision of the measurement. Twenty-four centres in Europe and North America were
provided with sets of rivaroxaban calibrators (0, 41, 209 and 422 ng/ml) and a set
of rivaroxaban pooled human plasma controls (20, 199 and 662 ng/ml; the concentrations
were unknown to the participating laboratories). The evaluation was carried out over
10 days by each laboratory using local anti-factor Xa reagents as well as the centrally
provided reagent, a modified STA® Rotachrom® assay. A calibration curve was produced each day, and the day-to-day precision was
evaluated by testing three human plasma controls. When using the local anti-factor
Xa reagents, the mean rivaroxaban concentrations (measured/actual values) were: 17/20,
205/199 and 668/662 ng/ml, and the coefficient of variance (CV) was 37.0%, 13.7% and
14.1%, respectively. When the modified STA Rotachrom method was used, the measured/actual
values were: 18/20, 199/199 and 656/662 ng/ml, and the CV was 19.1%, 10.9% and 10.0%,
respectively. The results suggest that, by using rivaroxaban calibrators and controls,
the anti-factor Xa chromogenic method is suitable for measuring a wide range of rivaroxaban
plasma concentrations (20–660 ng/ml), which covers the expected rivaroxaban plasma
levels after therapeutic doses.
Keywords
Anti-factor Xa assay - calibrators and controls - plasma levels - rivaroxaban