What is the goal Partial Thromboplastin Time (PTT) for a patient with Deep Vein Thrombosis (DVT) on heparin therapy?

Goal PTT for DVT Patients on Heparin Therapy

For patients with deep vein thrombosis (DVT) on unfractionated heparin therapy, the goal activated partial thromboplastin time (aPTT) should be 60-85 seconds, which corresponds to a plasma heparin level of 0.2 to 0.4 U/mL by protamine titration or 0.35 to 0.7 U/mL in terms of anti-factor Xa activity. 1

Therapeutic Range and Monitoring

• The therapeutic aPTT range of 60-85 seconds is associated with the lowest risk of recurrent venous thromboembolism in patients with DVT 1
• Studies have shown that patients with subtherapeutic aPTT values (<50 seconds) have a 15-fold increased risk of recurrent venous thromboembolism 1
• aPTT should be measured 6 hours after the initial bolus dose of heparin, and the continuous IV dose should be adjusted according to the result 1
• Despite its limitations, aPTT remains the most convenient and most frequently used method for monitoring the anticoagulant response to heparin 1

Dosing and Adjustment Protocols

• Initial dosing for DVT treatment typically involves an 80 U/kg bolus, followed by 18 U/kg/h continuous infusion 1
• Dose adjustments should follow established nomograms based on aPTT results 1:
  • aPTT <35 seconds: 80 U/kg bolus, then increase infusion by 4 U/kg/h
  • aPTT 35-45 seconds: 40 U/kg bolus, then increase infusion by 2 U/kg/h
  • aPTT 46-70 seconds: No change
  • aPTT 71-90 seconds: Decrease infusion rate by 2 U/kg/h
  • aPTT >90 seconds: Interrupt infusion for 1 hour, then decrease rate by 3 U/kg/h

Important Considerations

• The therapeutic range must be adapted to the responsiveness of the specific aPTT reagent used by your laboratory, as different reagents have varying sensitivities to heparin 1
• Pharmacokinetic limitations of heparin include variable anticoagulant response due to binding to plasma proteins, proteins released from platelets, and endothelial cells 1
• Heparin resistance may occur in some patients, requiring higher doses to achieve therapeutic aPTT levels 1
• The FDA label for heparin indicates that dosage is considered adequate when the aPTT is 1.5 to 2 times normal 2

Common Pitfalls to Avoid

• Failing to recognize that the therapeutic range varies with the responsiveness of the aPTT reagent to heparin 1
• Not monitoring aPTT at appropriate intervals (6 hours after bolus dose and then daily) 1
• Overlooking the need to adjust dosing regimens when heparin is combined with thrombolytic therapy or platelet GP IIb/IIIa antagonists 1
• Ignoring the potential for heparin-induced thrombocytopenia (HIT), which requires periodic monitoring of platelet counts throughout therapy 1
• Excessive anticoagulation (aPTT >90 seconds) increases bleeding risk without providing additional antithrombotic benefit 1

Alternative Approaches

• Low molecular weight heparin (LMWH) is now often preferred over unfractionated heparin for DVT treatment due to more predictable pharmacokinetics and reduced need for monitoring 3
• When using LMWH, routine aPTT monitoring is not required in most patients 3
• For patients transitioning to warfarin, heparin should overlap with warfarin for at least 5-7 days until the INR is in the therapeutic range (2.0-3.0) for 2 consecutive days 1