What is the therapeutic level of activated partial thromboplastin time (aPTT) for a patient on heparin (unfractionated heparin) gtt (intravenous infusion) for atrial fibrillation (AFib) before transitioning to Eliquis (apixaban)?

Therapeutic aPTT Range for Patients on Heparin for Atrial Fibrillation Before Transitioning to Apixaban

For patients with atrial fibrillation on unfractionated heparin (UFH) infusion before transitioning to apixaban, the target aPTT should be 1.5-2.5 times the control value, typically corresponding to 45-75 seconds depending on institutional control values. 1

Understanding the Therapeutic Range

The therapeutic range for UFH monitored by aPTT corresponds to heparin levels of 0.3-0.7 IU/mL by anti-factor Xa assay 2, 1. This range has been established to provide effective anticoagulation while minimizing bleeding risk.

Key points about the therapeutic range:

• The American College of Chest Physicians recommends a therapeutic aPTT ratio between 1.5 and 2.5 times the control value 2
• This typically translates to approximately 45-75 seconds, though the exact values depend on your institution's control values 2
• The therapeutic range correlates with heparin levels of 0.3-0.7 IU/mL by anti-factor Xa assay 1

Monitoring Protocol

When monitoring patients on heparin for atrial fibrillation:

1. Obtain baseline aPTT before starting heparin infusion
2. Check first aPTT 4-6 hours after initiating heparin or after any dose adjustment 1
3. Continue monitoring every 6 hours until two consecutive therapeutic values are achieved
4. Once stable, reduce monitoring to daily checks 1
5. Always recheck aPTT if clinical status changes (bleeding, recurrent symptoms, hemodynamic instability) 2

Important Considerations

Reagent Variability

aPTT results can vary significantly between laboratories due to differences in reagents and coagulometers 2:

• With the same heparin concentration (0.3 units/mL), aPTT results can range from 48 to 108 seconds depending on the reagent 2
• Each institution should calibrate their therapeutic range based on their specific reagents and equipment 3

Transitioning to Apixaban

When transitioning from heparin to apixaban:

• Discontinue heparin infusion
• Start apixaban immediately after stopping heparin 4
• No overlap period is necessary, unlike when transitioning to warfarin

Special Situations

Heparin Resistance

Some patients may exhibit heparin resistance, requiring unusually high doses to achieve therapeutic aPTT 2, 1:

• If a patient requires ≥35,000 units/day of heparin without achieving therapeutic aPTT
• Consider monitoring with anti-Xa levels (target range 0.35-0.7 units/mL) instead of aPTT 5
• Causes include antithrombin deficiency, increased heparin clearance, elevated factor VIII or fibrinogen levels 1

Dosing Adjustments

If aPTT is subtherapeutic or supratherapeutic, adjust the dose according to a standardized protocol 1:

• For aPTT <35 seconds: 80 U/kg bolus; increase infusion by 4 U/kg/hour
• For aPTT 35-45 seconds: 40 U/kg bolus; increase infusion by 2 U/kg/hour
• For aPTT 46-70 seconds: No changes (therapeutic range)
• For aPTT 71-90 seconds: Decrease infusion by 2 U/kg/hour
• For aPTT >90 seconds: Interrupt infusion for 1 hour, then decrease by 3 U/kg/hour

Avoiding Common Pitfalls

1. Reagent variability: Don't assume the same aPTT target across different institutions 2
2. Delayed monitoring: Failure to check aPTT within 4-6 hours after starting therapy can lead to under or over-anticoagulation 1
3. Ignoring clinical changes: Always reassess aPTT if the patient's clinical status changes 2
4. Inappropriate dosing: For atrial fibrillation, research suggests initial heparin infusion rates of 9.7-11.0 U/kg/hour without a bolus may result in therapeutic anticoagulation with lower bleeding risk 6

By maintaining the appropriate therapeutic aPTT range and following proper monitoring protocols, you can ensure effective anticoagulation for your atrial fibrillation patient while minimizing bleeding risk before transitioning to apixaban.