Table 1.

Anti-Xa Levels and Apixaban Concentrations for a Patient Who Also Received Carbamazepine

	Level or Concentration
Variable	While Taking Carbamazepine	While Not Taking Carbamazepine	Test Method or Calculation
Trough
Heparin level, local testing	0.84 U/mL (13:23 h since last apixaban dose)	0.63 U/mL (13:18 h since last apixaban dose)	Biophen heparin 6 assay
Apixaban concentration, local calculation	62 ng/mL	45 ng/mL	Apixaban = (heparin – 0.0482)/0.0128
Apixaban concentration, Hamilton laboratory	64 ng/mL	46 ng/mL	STA-Liquid Anti-Xa assay calibrated with STA-Apixaban Calibrator (reference range 22–230 ng/mL)
Peak
Heparin level, local testing	1.47 U/mL (2:29 h after apixaban dose)	1.27 U/mL (2:23 h after apixaban dose)	Biophen heparin 6 assay
Apixaban concentration, local calculation	111 ng/mL	95 ng/mL	Apixaban = (heparin – 0.0482)/0.0128
Apixaban concentration, Hamilton laboratory	110 ng/mL	92 ng/mL	STA-Liquid Anti-Xa assay calibrated with STA-Apixaban calibrator (reference range 59–321 ng/mL)