Coagulation

Definition

Coagulation is the complex enzymatic cascade by which liquid blood transforms into a stable gel (clot) to prevent hemorrhage. The cascade has intrinsic, extrinsic, and common pathways, ultimately producing fibrin to stabilize the platelet plug.

Key Laboratory Tests

• PT/INR: Extrinsic pathway (monitors warfarin). Therapeutic INR: 2 to 3 (most indications); 2.5 to 3.5 for mechanical valves.
• aPTT: Intrinsic pathway (monitors heparin). Therapeutic: 1.5 to 2.5 × control.
• Platelets: 150,000 to 400,000/µL. Spontaneous bleeding risk less than 20,000.
• Fibrinogen: 200 to 400 mg/dL.
• D-dimer: Elevated in DIC, PE, DVT.

Anticoagulant Antidotes

Warfarin: Vitamin K. Heparin: Protamine sulfate. Direct oral anticoagulants: andexanet alfa (rivaroxaban, apixaban), idarucizumab (dabigatran).

Nursing Considerations

Implement bleeding precautions for therapeutic anticoagulation: soft toothbrush, electric razor, avoid IM injections, fall prevention. Monitor labs per protocol.

NCLEX Relevance

Must memorize PT/INR vs aPTT and their antidotes.