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Difficulty: EasyMonitoring and Treatment Evaluation

A 58-year-old man is hospitalized with an acute deep vein thrombosis in his right leg. He is promptly started on a continuous intravenous infusion of unfractionated heparin. The nursing staff is instructed to draw blood every six hours to adjust the infusion rate according to a standard hospital protocol. Which of the following laboratory parameters is the most appropriate to monitor and titrate this therapy?

  1. Activated partial thromboplastin timeAnswer
  2. B
    International normalized ratio
  3. C
    D-dimer concentration
  4. D
    Bleeding time
  5. E
    Factor VIII activity level

Answer

Activated partial thromboplastin time is the standard parameter used to monitor and titrate continuous unfractionated heparin infusions.
The correct answer is activated partial thromboplastin time. Unfractionated heparin exerts its anticoagulant effect by binding to and potentiating antithrombin, which rapidly inactivates thrombin (factor IIa) and factor Xa, as well as other intrinsic pathway factors. Because its most pronounced effect is on the intrinsic coagulation pathway, the activated partial thromboplastin time is the standard, widely available laboratory parameter used to safely monitor its anticoagulant effect and dictate titration of the continuous infusion rate.

Step-by-Step Solution

1
Identify the specific medication administered to the patient.
The patient is receiving a continuous intravenous infusion of unfractionated heparin.
Different anticoagulant medications target different parts of the coagulation cascade and require different monitoring parameters.
2
Determine the appropriate laboratory monitoring test for this medication.
Unfractionated heparin is monitored using the activated partial thromboplastin time.
Heparin primarily enhances the activity of antithrombin, which subsequently inhibits factors in the intrinsic and common pathways (especially factor IIa and Xa). The intrinsic pathway is clinically measured by the activated partial thromboplastin time.

Key Concept

Monitoring continuous unfractionated heparin therapy requires serial measurement of the activated partial thromboplastin time to ensure therapeutic efficacy and minimize hemorrhage risk.
Estimated Time:45s
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Topics

Monitoring and Treatment Evaluation

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