In this episode, I’ll discuss using heparin anti-Xa levels to evaluate apixaban, rivaroxaban, fondaparinux, and danaparoid levels.
Anti-Xa inhibitors such as apixaban, rivaroxaban, fondaparinux, and danaparoid do not have readily available assays, yet there is often a clinical need to determine their presence or absence. Because heparin anti-Xa assays are overly sensitive to other Xa inhibitors, they cannot be used reliably to differentiate between therapeutic and supratherapeutic levels of anti-Xa inhibitors.
However, a low heparin anti-Xa level may be clinically useful to identify patients that do not have relevant concentrations of Xa inhibitors present. This could be used to inform whether an invasive procedure or surgery with a high bleeding risk could be undertaken in a patient previous on a Xa inhibitor.
Researchers recently published such information in Anesthesia and Analgesia.
Clinically relevant concentrations of apixaban, rivaroxaban, fondaparinux, and danaparoid were identified, and a heparin anti-Xa level cutoff was established in a derivation cohort which was then validated in a separate patient cohort.
The authors found that with over 96% accuracy, their heparin anti-Xa cutoffs could identify patients which no longer had relevant concentrations of Xa inhibitors.
The cutoff values for screening for relevant concentrations of Xa inhibitors were as follows:
For apixaban, a heparin anti-Xa of 0.2 or less identified a patient without relevant concentrations.
For rivaroxaban, a heparin anti-Xa of 0.3 or less.
For fondaparinux and danaparoid, a heparin anti-Xa level less than 0.1.
These heparin anti-Xa level cutoffs can easily be put into practice for patients scheduled to undergo invasive procedures with high bleeding risk to identify those who no longer have clinically relevant levels of theXa inhibitor present.
To access my free download area with 20 different resources to help you in your practice, go to pharmacyjoe.com/free.
If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.
Are there assay differences for heparin AntiXa levels that would lead to invalid cut-offs using the values found in the trial?
That is a great question! To my knowledge, anti-Xa is not like aPTT where the levels are institution/reagent-specific. However, it might be possible for there to be a difference between chromogenic and clotting-based assays.
If you had an aphasic stroke patient with apixaban on the med list and uncertain adherence, would you use a low anti-Xa to recommend thrombolysis?
Hi Cory! I think if I had a patient like that, an anti-Xa below the threshold could be used to justify that a thrombolytic could be considered.