What laboratory parameters should be monitored in an adult or geriatric patient with a history of thromboembolic events or risk factors, taking Eliquis (apixaban)?

Laboratory Monitoring for Patients on Eliquis (Apixaban)

Patients on Eliquis do not require routine monitoring of anticoagulation effect, but renal function, complete blood count, and liver function tests should be checked before initiation and periodically during treatment. 1, 2

Baseline Laboratory Assessment

Before starting Eliquis, the following labs must be obtained 1:

• Complete blood count (CBC) - to establish baseline hemoglobin and platelet count
• Serum creatinine with calculated creatinine clearance (CrCl) using Cockcroft-Gault or MDRD formula - essential for dose adjustment decisions
• Liver function tests - transaminases and bilirubin
• PT/INR and aPTT - to establish baseline coagulation parameters

Ongoing Monitoring Requirements

Renal Function Monitoring

Renal function is the most critical parameter requiring regular monitoring 2:

• At least annually for patients with normal renal function (CrCl >50 mL/min) 2
• Every 3-6 months for high-risk patients including 2:
  • Elderly patients (age ≥80 years)
  • Baseline impaired renal function (CrCl 30-50 mL/min)
  • Conditions that may affect renal function (heart failure, diabetes, hypertension)
• More frequently when acute illness develops or new medications that affect kidney function are started 2

Complete Blood Count Monitoring

• Every 2-4 weeks if patient develops thrombocytopenia (platelet count <150 × 10^9/L) or anemia 3
• Consider dose reduction to 2.5 mg twice daily if platelet count is 50-131 × 10^9/L with concurrent anemia (Hgb <10 g/dL) 3
• Consider temporary discontinuation if platelet count drops below 50 × 10^9/L 3

Liver Function Tests

• Baseline assessment required 1
• Periodic monitoring in patients with known liver disease or elevated baseline transaminases 1

Dose Adjustment Criteria Based on Lab Values

Reduce dose to 2.5 mg twice daily if patient has at least TWO of the following 1, 4:

• Age ≥80 years
• Body weight ≤60 kg
• Serum creatinine ≥1.5 mg/dL

For severe renal impairment (CrCl 15-29 mL/min), dose reduction may be needed, though data are limited 2

Laboratory Tests That Are NOT Routinely Needed

Standard coagulation tests (PT/INR, aPTT) are not recommended for routine monitoring because 1, 2, 5:

• PT and aPTT show variable sensitivity depending on reagent used
• These tests cannot accurately quantify apixaban levels
• No therapeutic range has been established for these tests with apixaban

Special Situations Requiring Laboratory Assessment

Suspected Bleeding or Need for Urgent Surgery

When quantification of apixaban effect is needed 1, 6:

• Anti-Factor Xa assay with apixaban-specific calibrators - most accurate test (linear correlation r² = 0.78-1.00) 6
• PT/INR - may show prolongation but insufficient for accurate quantification 1, 5
• aPTT - less sensitive than PT for factor Xa inhibitors 6
• Thrombin time (TT) - not useful for apixaban (only for dabigatran) 1

The International Society on Thrombosis and Haemostasis recommends considering reversal for 1:

• Serious bleeding with DOAC level >50 ng/mL
• High bleeding risk procedures with DOAC level >30 ng/mL

Drug Interaction Assessment

Monitor for interactions with 1, 2:

• Strong dual P-glycoprotein and CYP3A4 inhibitors (ketoconazole, itraconazole, ritonavir, clarithromycin) - reduce apixaban dose to 2.5 mg twice daily if patient already on 5 mg twice daily; avoid if already on 2.5 mg twice daily 1
• Strong P-glycoprotein and CYP3A4 inducers (rifampin, phenytoin, carbamazepine, St. John's wort) - avoid concomitant use as these decrease apixaban efficacy 1

Perioperative Laboratory Management

Before elective surgery 1, 2, 4:

• Discontinue 48 hours prior for moderate-to-high bleeding risk procedures 4
• Discontinue 24 hours prior for low bleeding risk procedures 4
• Check renal function to determine appropriate timing (longer interruption needed if CrCl <50 mL/min) 1
• No bridging anticoagulation typically required 1, 4

Common Pitfalls to Avoid

Do not assume no monitoring means no follow-up - while coagulation monitoring isn't required, clinical monitoring and renal function assessment remain essential 2

Do not use PT/INR or aPTT to guide dosing decisions - these tests are unreliable for apixaban quantification 1, 5

Do not forget to reassess renal function during acute illness - conditions like dehydration, sepsis, or heart failure exacerbation can rapidly worsen kidney function and increase bleeding risk 2

Do not order anti-Factor Xa assays without apixaban-specific calibrators - generic anti-Xa assays calibrated for heparin will not accurately measure apixaban levels 1, 6