Correlation between dilute Russell's viper venom time (dRVVT) and apixaban concentrations: Potential utility and...

Apixaban prolongs the dilute Russell's viper venom time (dRVVT), which may serve as a rapid surrogate for identifying clinically relevant drug concentrations in urgent settings.

To evaluate the correlation between dRVVT and apixaban concentration, and to establish cut-off values for clinically relevant thresholds (≥ 30 and ≥ 50 ng/mL).

This cross-sectional study included 104 patients receiving apixaban. Normalized dRVVT screening and confirmation ratios were compared with chromogenic anti-factor Xa-based apixaban concentrations. Correlations were evaluated using Spearman's rank correlation coefficient (ρ). The ROC curve analysis with the Youden index was performed to identify optimal diagnostic cut-offs.

The median apixaban concentration was 116.3 ng/mL (IQR, 78.9-177.2), with ≥ 30 ng/mL observed in 96.2%. Moderate correlations were observed between dRVVT ratios and apixaban concentrations for both screening and confirmatory assays (ρ = 0.675 [95% CI, 0.554-0.768] and 0.713 [95% CI, 0.604-0.797], respectively). Both dRVVT ratios showed comparable discriminative ability for detecting concentrations ≥ 50 ng/mL (AUC, 0.885 vs. 0.892; P = 0.690) and ≥ 30 ng/mL (AUC, 0.956 vs. 0.975; P = 0.446). Optimal cut-off values (screening/confirmation) for ≥ 50 ng/mL were 1.33/1.42, with sensitivities of 82.8%/84.9% and specificities of 90.9%. For ≥ 30 ng/mL, cut-offs of 1.12/1.16 provided sensitivities of 92.0%/96.0% and specificities of 100%.

dRVVT assays correlate moderately with apixaban concentrations. dRVVT may support semi-quantitative assessment and rule-in of apixaban exposure; however, it cannot reliably exclude low drug levels. The low prevalence of subthreshold concentrations may limit specificity precision, warranting caution in borderline or high-risk clinical scenarios.

Thai Clinical Trials Registry: TCTR20250124009.