What lab tests should be done for an elderly nursing home patient with Deep Vein Thrombosis (DVT) on anticoagulation therapy such as apixaban (Eliquis) or rivaroxaban (Xarelto)?

Laboratory Monitoring for Elderly Nursing Home Patients on Apixaban or Rivaroxaban for DVT

For elderly nursing home patients on apixaban (Eliquis) or rivaroxaban (Xarelto) for DVT, baseline laboratory testing should include complete blood count, PT, aPTT, serum creatinine with calculated creatinine clearance (using Cockcroft-Gault formula), liver transaminases, and bilirubin before initiating therapy, with periodic renal function monitoring during treatment. 1

Baseline Laboratory Assessment (Before Starting Therapy)

Required baseline tests include: 1

• Complete blood count (CBC) to establish baseline hemoglobin and platelet levels 1
• Prothrombin time (PT) and activated partial thromboplastin time (aPTT) to assess baseline coagulation status 1
• Serum creatinine with calculated creatinine clearance (CrCl) using Cockcroft-Gault or MDRD formula 1
• Liver function tests including transaminases and bilirubin 1

The International Society on Thrombosis and Haemostasis emphasizes that CrCl calculation is mandatory before prescribing DOACs, as renal function directly impacts drug clearance and dosing decisions 1.

Renal Function Monitoring During Treatment

Periodic renal function monitoring is essential because: 1

• Rivaroxaban has 33% renal clearance and requires dose reduction from 20 mg to 15 mg once daily when CrCl is 15-30 mL/min 1
• Apixaban has 27% renal clearance, making it preferable in patients with renal impairment 2
• Elderly patients are at higher risk for worsening renal function, which can lead to drug accumulation 1
• The American College of Chest Physicians recommends dose reduction for rivaroxaban in patients with CrCl between 15-30 mL/min 1

Monitoring frequency should be increased when: 1

• Baseline CrCl is 30-50 mL/min (moderate renal impairment) 1
• Patient is ≥80 years old 1
• Patient develops acute illness or dehydration that could affect renal function 1
• Concomitant nephrotoxic medications are prescribed 1

Routine Monitoring Parameters

Unlike warfarin, DOACs do not require routine coagulation monitoring for dose adjustment. 1 However, the American College of Chest Physicians states that PT and aPTT are not validated for monitoring therapeutic effect of rivaroxaban or apixaban and should not be used for dose adjustments 1.

Periodic monitoring should include: 1

• Renal function reassessment at least annually, or more frequently (every 3-6 months) in patients with CrCl 30-50 mL/min or age ≥75 years 1
• Liver function tests if baseline abnormalities were present or if clinical signs of hepatotoxicity develop 1
• CBC if bleeding symptoms occur or as clinically indicated 1

Special Laboratory Considerations for Bleeding or Emergency Situations

When bleeding occurs or urgent procedures are needed, specific DOAC level testing may be valuable: 1

• Chromogenic anti-factor Xa assay (calibrated for rivaroxaban or apixaban) is the preferred quantitative test for factor Xa inhibitors 1
• Qualitative assessment: PT is more sensitive to rivaroxaban than aPTT, though neither should be used for therapeutic monitoring 1
• The 2023 World Society of Emergency Surgery guidelines recommend considering reversal agents only when DOAC levels are >50 ng/mL for serious bleeding or >30 ng/mL for high-risk procedures 1

Standard coagulation tests have limited utility: 1

• A normal PT does not exclude clinically relevant levels of factor Xa inhibitors 1
• PT and aPTT results depend on reagent sensitivity and timing relative to last dose 1
• Viscoelastic tests (ROTEM/TEG) may be helpful in trauma settings but are not routinely recommended 1

Contraindications Based on Laboratory Values

Absolute contraindications include: 1

• Rivaroxaban: CrCl <15 mL/min 1
• Apixaban: CrCl <15 mL/min 2
• Both drugs: Liver transaminases >2× upper limit of normal with coagulopathy, or Child-Pugh B/C cirrhosis 1

Drug Interaction Monitoring

Laboratory monitoring should be intensified when patients receive: 1

• Strong P-glycoprotein inhibitors (amiodarone, verapamil, clarithromycin) which increase DOAC bioavailability 1
• CYP3A4 inhibitors (for rivaroxaban specifically) such as ketoconazole or HIV protease inhibitors 1
• Concomitant antiplatelet agents, which increase bleeding risk without changing laboratory parameters 1

The British Society of Gastroenterology emphasizes that concomitant use of aspirin or NSAIDs with DOACs significantly increases bleeding risk and warrants more vigilant clinical monitoring 1.