A patient receiving intravenous unfractionated heparin infusion for pulmonary embolism is monitored with activated partial thromboplastin time (aPTT). Therapeutic anticoagulation corresponds to which aPTT target?
- A 1 to 1.5 times the control value
- B 3.5 to 5 times the control value
- C 1.5 to 2.5 times the control value ✓
- D aPTT is not useful; only anti-Xa levels are measured
Correct answer: C. 1.5 to 2.5 times the control value
Explanation
Unfractionated heparin is monitored by aPTT kept at 1.5 to 2.5 times control, equivalent to anti-Xa activity of 0.3 to 0.7 IU/mL. Below this range thrombosis risk persists; above it bleeding risk rises sharply. Anti-Xa assay is reserved for situations where aPTT is unreliable such as lupus anticoagulant or massive factor deficiency, not routine monitoring.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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