Effective today, May 14, 2019, the University of Iowa Hospitals and Clinics core laboratory will begin running assays for rivaroxaban (Epic LAB8857) and apixaban (Epic LAB8858) quantification. Both are chromogenic anti-Xa assays. Details on the new assays are as follows:

Specimen Type: 2.7 mL light blue top tube (full draw) or 1.8 mL light blue top tube (full draw)

Test Result Availability: Within 1-2 hours of specimen receipt in the laboratory

The measuring range for apixaban is 20-550 ng/mL. The measuring range for rivaroxaban is 20-450 ng/mL. Therapeutic ranges have not been established for either drug. Therapeutic ranges derived from published literature are variable and are not well correlated with safety, efficacy, or clinical outcomes. Therefore, they should not be used to determine if a patient is adequately or overly anticoagulated. The use of these tests should be limited to the following:

1. Measurement of anti-Xa activity in patients undergoing emergent/urgent surgical procedures or with life threatening bleeding associated with rivaroxaban or apixaban use
2. Assessment of level in a patient who is expected to have been non-adherent/non-compliant

In addition, these assays measure all anti-Xa activity in the sample, and, therefore, are not specific for apixaban or rivaroxaban. Drugs with anti-Xa activity (e.g., heparin, enoxaparin, edoxaban, betrixaban) will cross-react to give a measurable concentration of apixaban or rivaroxaban.

Questions should be directed to Carol Holman, MD, 356-3981.