Evaluation of the anti-factor Xa chromogenic assay for the measurement of rivaroxaban plasma concentrations using calibrators and controls

Abstract

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.

Laboratory Measurement of the Anticoagulant Activity of the Non–Vitamin K Oral Anticoagulants

“…Investigators found a greater degree of assay imprecision at higher rivaroxaban concentrations (800 ng/ml) in one study (45). In a multicenter study, both intra- and interlaboratory precision were satisfactory except at the lower limit of detection (20 ng/ml); use of a centrally distributed reagent reduced interlaboratory variability (46). Mathematical modeling also decreased interassay variability resulting from different sensitivities of individual reagents to rivaroxaban (40).…”

“…The correlation was less robust at concentrations <100 ng/mL (49). However, Samama and colleagues demonstrated that low rivaroxaban concentrations could be measured with a modified anti-Xa test using less diluted samples (46). Investigators found a greater degree of assay imprecision at higher rivaroxaban concentrations (800 ng/ml) in one study (45).…”

Pharmacodynamics and pharmacokinetics during the transition from warfarin to rivaroxaban: a randomized study in healthy subjects

“…Studies have indicated that the anti-factor Xa chromogenic method is the best test for assessing rivaroxaban exposure when used in conjunction with rivaroxaban calibrators and controls 20, if a quantitative assessment of rivaroxaban exposure is required in certain clinical situations. It should be emphasized that, although rivaroxaban affects the PT/INR, this system is not suitable for assessing the anticoagulant intensity of rivaroxaban 6,7.…”

New oral anticoagulants in patients with nonvalvular atrial fibrillation: a review of pharmacokinetics, safety, efficacy, quality of life, and cost effectiveness

“…The target specific inhibitors dabigatran, rivaroxaban and apixaban represent a new class of anticoagulants that can not be monitored with global coagulation tests due there is not a predictable linear relationship between laboratory value and drug concentration 49–56. Chromogenic anti-factor Xa assays have been demonstrated to have the potential for accurate measurement of plasma concentrations of the direct factor Xa inhibitors 57–60. However, the threshold values of drug concentrations and the degree of prolongation that might still be assumed as safe must be defined.…”