Alternative Monitoring for Antithrombotic Agents at UWMC
Heparin Activity (Anti factor Xa level)
Used to monitor low molecular weight heparins; or instead of aPTT in patients with antiphospholipid antibodies that might interfere with aPTT, or in patients with presumed heparin resistance as measured by aPTT.
- Therapeutric range for low molecular weight heparins (LMWH):
- Peak for twice daily SQ dosing: 0.5-1 units/mL (3-4 hours after dose)
- Peak for once daily SQ dosing: 1-1.5 units/mL (3-4 hours after dose)
- Trough: < 0.5 units/mL
- Therapeutric range for IV unfractionated heparin: 0.3-0.7 units/mL
- Test order code: HEPACT
- Specimen collection: 5mL blue top
Direct Thrombin Inhibitor Assay
Used instead of aPTT to assess DTI therapy. Preferred over aPTT due to better sensitivity, and is not affected by antiphospholipid antibodies. Cost, turn-around time and 24/7 availablity at UWMC are similar to aPTT.
- Therapeutic range
- For argatroban: 60-100 seconds
- For bivalirudin: 60-90 seconds
- For lepirudin: 90-160 seconds
- Test order code: DTI
- Specimen collection: 3mL or 5mL blue top
Chromogenic Factor X
Used instead of INR in patients with antiphospholipid antibodies that might interfere with INR, or in patients on concurrent direct thrombin inhibitors that might interfere with INR.
- Therapeutic range for warfarin: 45-25% = INR 2-4
- Test order code: CHRF10
- Specimen collection: 3mL or 5mL light top tube (citrate)