Lecture Notes: aPTT Blood Test

Introduction

• Presenter: Sarah
• Topic: aPTT Blood Test
• Accompanying material: Free quiz available to test knowledge on this content.

What is aPTT?

• aPTT stands for Activated Partial Thromboplastin Time.
• It is a blood test used to assess how quickly blood clots.
• Collection method:
  • Blood is drawn from a patient's vein.
  • Placed in a special tube.
  • Sent to a lab for testing.
• Useful in diagnosing bleeding disorders by examining specific clotting factors in the coagulation cascade.

Monitoring & Use with Heparin

• aPTT is crucial for monitoring patients on Heparin.
  • Heparin is an indirect thrombin inhibitor.
  • It enhances antithrombin 3, preventing thrombin activation.
  • This action prevents fibrinogen from converting to fibrin, thereby delaying clot formation.

Coagulation Cascade

• Purpose: To prevent blood loss from the vascular system after injury.
• Components:
  • Intrinsic Pathway: Activated by internal vascular damage.
  • Extrinsic Pathway: Activated by external injury.
  • Common Pathway: Convergence of intrinsic and extrinsic pathways for clot formation.
• aPTT assesses the Intrinsic Pathway, focusing on clotting factors 12, 11, 9, 8.
  • Also evaluates the Common Pathway (factors 1, 2, 5, 10).

Comparison with PT/INR

• PT/INR measures the Extrinsic Pathway.
• aPTT specifically looks at the intrinsic pathway and some common pathway factors.

aPTT Measurement & Normal Ranges

• Measured in seconds.
• Difference between aPTT and PTT:
  • Both measure intrinsic and common pathways.
  • aPTT includes an activator agent to speed up clotting time.
• Normal Range: Generally 30-40 seconds but varies by lab.
• Therapeutic Range for Heparin Therapy: 1.5 to 2.5 times the normal value.
  • Typically around 60-70 seconds.

Conclusion

• Summary of aPTT's importance in assessing coagulation and monitoring heparin therapy.
• Reminder to take the quiz for further assessment of understanding.