A client is receiving IV heparin for deep vein thrombosis. Which laboratory value should the nurse monitor to assess therapeutic effectiveness?

HEPARIN is an anticoagulant that works by activating antithrombin III, which in turn inhibits thrombin and factor Xa — interrupting the intrinsic and common coagulation pathways. MONITORING: IV HEPARIN is monitored with aPTT (activated partial thromboplastin time); normal aPTT = 25-40 seconds; THERAPEUTIC aPTT for heparin = 60-100 seconds (1.5-2.5 × control); aPTT is checked every 6 hours until stable, then daily. WARFARIN (Coumadin) is monitored with PT/INR (prothrombin time/International Normalized Ratio) — warfarin affects the extrinsic pathway (factor VII and others). PT/INR DOES NOT ACCURATELY REFLECT HEPARIN EFFECT. HEPARIN TOXICITY SIGNS: bleeding (easy bruising, petechiae, hematuria, melena, hemoptysis, intracranial bleeding); prolonged oozing from IV sites or skin punctures. ANTIDOTE: PROTAMINE SULFATE reverses heparin (1 mg protamine per 100 units of heparin); given slowly IV (can cause hypotension and anaphylaxis). HEPARIN-INDUCED THROMBOCYTOPENIA (HIT): IMMUNE-MEDIATED adverse reaction; paradoxically causes THROMBOSIS (not bleeding) despite low platelets; onset 5-10 days after starting heparin; PLATELET COUNT monitored to detect HIT (platelet drop >50% from baseline is suspicious); treatment: STOP heparin immediately, switch to non-heparin anticoagulant (argatroban, bivalirudin, fondaparinux). LOW MOLECULAR WEIGHT HEPARIN (LMWH — enoxaparin/Lovenox): monitored with anti-Xa level; does NOT require routine aPTT monitoring for most patients; subcutaneous injection; easier outpatient use. PN ROLE: monitor aPTT; assess for bleeding; hold pressure on IV sites; teach patient about bleeding precautions (soft toothbrush, electric razor, fall prevention); report any aPTT out of therapeutic range to RN immediately.