A 55-year-old woman is started on intravenous unfractionated heparin infusion for pulmonary embolism. Which laboratory parameter should be used to titrate her dose?
- A Activated partial thromboplastin time ✓
- B Prothrombin time (INR)
- C Anti-factor Xa level
- D Bleeding time
Correct answer: A. Activated partial thromboplastin time
Explanation
Unfractionated heparin potentiates antithrombin inhibition of both thrombin and factor Xa, so its therapeutic effect prolongs the aPTT, and dosing is titrated to roughly 1.5 to 2.5 times the control value. INR monitors warfarin, not heparin. Anti-factor Xa levels are used to monitor low molecular weight heparin, where the aPTT is insensitive. Bleeding time reflects primary haemostasis and does not change predictably with heparin.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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