What laboratory test monitors the effect of heparin therapy?

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Multiple Choice

What laboratory test monitors the effect of heparin therapy?

Explanation:
The test most suitable for monitoring unfractionated heparin therapy measures how long it takes blood to clot after initializing an intrinsic pathway reaction. Heparin works by boosting antithrombin III, which inhibits thrombin and several clotting factors, thereby slowing clot formation. The activated partial thromboplastin time (aPTT) is sensitive to these intrinsic pathway factors and their inhibition, so it directly reflects the anticoagulant effect of heparin. Clinically, the aPTT is kept in a therapeutic range (often about 1.5–2.5 times the patient’s control value) to balance preventing clots with avoiding bleeding. Why the other tests aren’t used for this purpose: the PT assesses the extrinsic pathway and is more relevant to warfarin monitoring, not heparin. A CBC provides counts and hematologic status rather than clotting time. D-dimer indicates fibrin degradation and is used to evaluate suspected thrombosis or to monitor for clot breakdown, not to gauge anticoagulant effect.

The test most suitable for monitoring unfractionated heparin therapy measures how long it takes blood to clot after initializing an intrinsic pathway reaction. Heparin works by boosting antithrombin III, which inhibits thrombin and several clotting factors, thereby slowing clot formation. The activated partial thromboplastin time (aPTT) is sensitive to these intrinsic pathway factors and their inhibition, so it directly reflects the anticoagulant effect of heparin. Clinically, the aPTT is kept in a therapeutic range (often about 1.5–2.5 times the patient’s control value) to balance preventing clots with avoiding bleeding.

Why the other tests aren’t used for this purpose: the PT assesses the extrinsic pathway and is more relevant to warfarin monitoring, not heparin. A CBC provides counts and hematologic status rather than clotting time. D-dimer indicates fibrin degradation and is used to evaluate suspected thrombosis or to monitor for clot breakdown, not to gauge anticoagulant effect.

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