A universal anti‐Xa assay for rivaroxaban, apixaban, and edoxaban measurements: method validation, diagnostic accuracy and external validation

Figures

• 

  Fig 1. Flow of the patients. A prospective, multicentre cross‐sectional study was conducted to test the hypothesis that a universal anti‐Xa assay would accurately measure rivaroxaban, apixaban, or edoxaban drug levels in clinical practice, and correctly predict clinically relevant drug levels.

• 

  Fig 2. Low‐molecular‐weight heparin (LMWH)‐calibrated anti‐Xa activity in standardised plasma samples spiked with rivaroxaban, and apixaban, as measured in seven haemostasis laboratories. Results of pilot study 1 are shown; Spearman correlation coefficient was 1·0 in all laboratories.

• 

  Fig 3. Measurements of a universal, low‐molecular‐weight heparin (LMWH)‐calibrated anti‐Xa assay in relation to drug concentrations in a multicentre cross‐sectional study conducted in clinical practice (n = 867). Drug concentrations were determined using ultra‐high performance liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). Of the patients, 375 were taking rivaroxaban, 426 apixaban and 66 edoxaban. Spearman correlation coefficient was 0·99 for rivaroxaban (95% CI 0·98–0·99), 0·97 for apixaban (95% CI 0·96–0·97), and 0·98 for edoxaban (95% CI 0·95–0·99).

• 

  Fig 4. Diagnostic accuracy of a universal, low‐molecular‐weight heparin (LMWH)‐calibrated anti‐Xa assay for the measurement of rivaroxaban, apixaban, and edoxaban drug concentrations as determined in a multicentre cross‐sectional study in clinical practice (n = 867). (A) Box plots illustrating the distribution of measurements (median, interquartile range, minimum to maximum, all results) at clinically relevant cut‐offs (> and < 30, 50, and 100 µg/l). (B) Receiver‐operating characteristic (ROC) curves showing the diagnostic accuracy. The area under the ROC curve was 0·99 for all cut‐offs. (C) Confusion matrices at each cut‐off. Drug levels of >30 µg/l were detected with a sensitivity of 96·2% (95% CI 94·4–97·4; cut‐off value 0·35 u/ml), drug levels of >50 µg/l with a sensitivity of 96·4% (95% CI 94·4–97·7; cut‐off value 0·58 u/ml) and drug levels of >100 µg/l with a sensitivity of 96·4% (95% CI 94·0–97·9; cut‐off value 1·14 u/ml). The specificities were 92·9% (95% CI 88·9–95·5), 93·3% (95% CI 90·1–95·5) and 92·0 (95% CI 89·4–94·0) respectively.

• 

  Fig 5. Results of an external validation of a universal, low‐molecular‐weight heparin (LMWH)‐calibrated anti‐Xa assay for the measurement of rivaroxaban, apixaban, and edoxaban (n = 666). (A) Box plots illustrating the distribution of measurements (median, interquartile range, minimum to maximum, all results) at clinically relevant cut‐offs (> and < 30, 50, and 100 µg/l). (B) Receiver‐operating characteristic (ROC) curves showing the diagnostic accuracy. The area under the ROC curve was 0·98 for all cut‐offs. (C) Confusion matrices at each cut‐off. Drug levels of >30 µg/l were detected with a sensitivity of 95·8% (95% CI 93·0–97·3), drug levels of >50 µg/l with a sensitivity of 97·4% (95% CI 95·4–98·6), and drug levels of >100 µg/l with a sensitivity of 94·8% (95% CI 91·4–97·1). The specificities were 85·9% (95% CI 80·3–90·2), 91·7% (95% CI 87·8–94·4) and 92·5% (95% CI 89·4–94·9), respectively.