What labs should be drawn to assess coagulation in a patient on Eliquis (apixaban)?

Laboratory Tests for Coagulation Assessment in Patients on Eliquis (Apixaban)

For patients on apixaban (Eliquis), the recommended coagulation test is a calibrated chromogenic anti-Factor Xa assay, which is the only reliable method to accurately assess the anticoagulant effect. 1

Primary Coagulation Tests for Apixaban Assessment

First-Line Test

• Chromogenic anti-Factor Xa assay calibrated specifically for apixaban
  • This is the gold standard test for quantitative measurement of apixaban levels
  • Provides accurate drug concentration measurements
  • Should be calibrated with apixaban-specific calibrators for best results 1

Alternative Tests When Anti-Xa Assay Is Not Available

• Uncalibrated anti-Xa assay (using LMWH or UFH calibration)
  • Can qualitatively detect presence of apixaban
  • Cannot provide accurate quantification but can exclude clinically relevant levels when below detection limit 1
• Prothrombin Time (PT)
  • Limited sensitivity to apixaban
  • A prolonged PT suggests presence of on-therapy or above on-therapy levels
  • Normal PT does NOT exclude clinically relevant apixaban levels 1
• Activated Partial Thromboplastin Time (aPTT)
  • Very insensitive to apixaban
  • Normal aPTT does NOT exclude clinically relevant drug levels 1

Interpretation of Test Results

Test	Interpretation
Anti-Xa assay (apixaban-calibrated)	Linear dose-response relationship with apixaban concentration
PT	Prolonged PT suggests apixaban effect but normal PT doesn't exclude it
aPTT	Insensitive; normal aPTT doesn't exclude apixaban presence

Important Clinical Considerations

1. Timing of blood collection is critical:

   • Document time of last apixaban dose relative to blood draw
   • Peak levels occur 3-4 hours after ingestion 2
   • Trough levels occur just before next scheduled dose

2. Therapeutic ranges:

   • Typical therapeutic range: 91-321 ng/mL for 5 mg twice daily dosing 3
   • Levels >50 ng/mL may contribute to bleeding risk 1

3. Limitations of standard coagulation tests:

   • PT/INR and aPTT show poor correlation with apixaban levels at therapeutic concentrations 4, 5
   • At therapeutic doses, changes in PT/INR and aPTT are minimal and highly variable 2

Special Situations

Suspected Overdose or Bleeding

For patients with suspected overdose or active bleeding, obtain:

• Anti-Xa assay (apixaban-calibrated)
• Complete blood count
• Basic metabolic panel (especially creatinine)
• PT/INR and aPTT 1, 3

Urgent Surgery or Procedures

For patients requiring urgent procedures:

• Anti-Xa assay (apixaban-calibrated) if available
• PT/INR and aPTT (recognizing limitations)
• Consider viscoelastic testing if available 6

Common Pitfalls to Avoid

1. Do not rely on PT/INR or aPTT alone to assess apixaban activity or guide reversal decisions 1

2. Do not assume normal coagulation tests mean absence of drug effect - standard tests are insensitive to apixaban 1, 4

3. Do not interpret anti-Xa results without considering timing of last dose and renal function 1

4. Avoid using tests calibrated for other anticoagulants (e.g., heparin calibrated anti-Xa) for quantitative assessment 1

In conclusion, while routine monitoring of apixaban is not required, when assessment of anticoagulant effect is needed, a chromogenic anti-Xa assay calibrated specifically for apixaban is the only reliable method. Standard coagulation tests like PT/INR and aPTT have significant limitations and should not be used to guide clinical decisions about apixaban therapy.