What are the indications for using heparin in inpatient and outpatient settings?

Indications for Heparin Use in Inpatient and Outpatient Settings

Heparin is indicated for both prophylaxis and treatment of thromboembolic disease, with inpatient use being standard for acute therapeutic anticoagulation requiring rapid onset and close monitoring, while outpatient use is primarily limited to low-molecular-weight heparin (LMWH) for selected stable patients with venous thromboembolism (VTE) or extended prophylaxis in high-risk populations. 1

Inpatient Indications

Therapeutic Anticoagulation (Full-Dose)

Unfractionated heparin (UFH) by continuous IV infusion is the preferred agent for acute thrombotic emergencies requiring immediate anticoagulation:

• Acute venous thromboembolism (DVT/PE) – IV heparin achieves therapeutic anticoagulation within minutes and directly prevents recurrent embolism, reducing mortality when therapeutic aPTT is reached within 24 hours (recurrence rate 2% vs 25% with delayed therapeutic levels) 2, 3
• Hemodynamically unstable pulmonary embolism – IV UFH is mandatory in patients with shock or hypotension, as LMWH has not been tested in unstable patients 4
• Acute coronary syndromes – In unstable angina or NSTEMI, IV heparin combined with aspirin reduces cardiovascular death and MI by approximately 30% compared to aspirin alone 3, 2, 5
• Atrial fibrillation with embolization 1
• Acute consumptive coagulopathies (DIC) 1
• Arterial and cardiac surgery – Prevention of clotting during procedures 1
• Peripheral arterial embolism – Both prophylaxis and treatment 1

Dosing for therapeutic anticoagulation: 80 U/kg IV bolus followed by 18 U/kg/hour continuous infusion, targeting aPTT 1.5–2.5 times control 2, 1

Prophylactic Anticoagulation (Low-Dose)

Pharmacological VTE prophylaxis is strongly recommended for acutely or critically ill medical inpatients at acceptable bleeding risk:

• Hospitalized medical patients – UFH 5,000 U subcutaneously every 8 hours, or LMWH (enoxaparin 40 mg once daily, dalteparin 5,000 U once daily) reduces DVT risk significantly 3
• Surgical patients – UFH 5,000 U given 2–4 hours preoperatively and every 8 hours thereafter, or LMWH at specified doses 3, 1
• Major abdominothoracic surgery – Prophylaxis should continue for at least 7–10 days, with extended prophylaxis up to 4 weeks considered for high-risk patients 3, 1
• Multiple trauma patients – LMWH (enoxaparin 30 mg every 12 hours) reduces DVT incidence from 44% to 31% compared to low-dose UFH 3
• Hip fracture surgery – Prophylaxis significantly reduces thrombosis rates 3

When bleeding risk is unacceptable, mechanical prophylaxis (intermittent pneumatic compression) should be used instead of pharmacological prophylaxis 3

Critical Monitoring Requirements

• aPTT monitoring: Every 4–6 hours during initiation, then daily once stable for IV heparin 2, 1
• Platelet counts: Monitor every 2–3 days from day 4 to day 14 to screen for heparin-induced thrombocytopenia (occurs in up to 5% of patients) 2, 4
• Renal function: Essential before LMWH use; if creatinine clearance <30 mL/min, reduce LMWH dose or switch to UFH with aPTT monitoring 4, 6

Outpatient Indications

Treatment of Stable VTE

LMWH administered at home is at least as safe and effective as inpatient UFH treatment for appropriately selected patients with DVT:

• Stable deep vein thrombosis – Level 1 evidence supports outpatient LMWH treatment with recurrent thrombosis rates of 0–9%, major bleeding 0–4%, and significant cost savings 3
• Selected stable pulmonary embolism – Limited evidence exists, but stable patients without hemodynamic compromise may be candidates 3

Patient selection criteria for outpatient treatment:

• No previous VTE or thrombophilic conditions
• No significant comorbidity
• Hemodynamically stable
• Adequate support services in place
• Likely to adhere to therapy
• No contraindications to anticoagulation 3

Dosing: Enoxaparin 1 mg/kg subcutaneously every 12 hours or 1.5 mg/kg once daily, overlapping with warfarin for minimum 5 days until INR 2.0–3.0 for 2 consecutive days 3, 4

Extended Prophylaxis Post-Discharge

Extended prophylaxis beyond hospital discharge is conditionally recommended only for specific high-risk populations:

• Cancer patients – Extended LMWH monotherapy (at 75–80% of initial dose) for 6 months is superior to warfarin, and anticoagulation should continue as long as active malignancy persists 4
• High-risk surgical patients – Consider extending prophylaxis for 3–4 weeks after discharge in patients undergoing major surgery (e.g., total hip replacement) 7

The American Society of Hematology strongly recommends AGAINST routinely extending pharmacological prophylaxis after hospital discharge in general medical patients 3

Outpatient Populations NOT Recommended for Routine Prophylaxis

• Long-term care residents – Conditional recommendation against routine VTE prophylaxis 3
• Outpatients with minor injuries – Conditional recommendation against routine prophylaxis 3
• Long-distance travelers – Only conditionally recommend graduated compression stockings or LMWH if at high VTE risk, not for routine use 3

Key Clinical Pitfalls to Avoid

Common errors that increase morbidity and mortality:

• Using fixed-dose UFH regimens – Consistently fail to achieve therapeutic anticoagulation in first 24 hours and are associated with 25% recurrence rate; always use weight-based dosing 2
• Stopping LMWH before day 5 – Increases recurrent PE risk even if INR is therapeutic 4
• Stopping LMWH after only one therapeutic INR – Requires INR 2.0–3.0 for 2 consecutive days 4
• Abrupt UFH cessation in acute coronary syndromes – Causes "heparin rebound" with hypercoagulability and clustering of ischemic events at median 9.5 hours post-cessation; LMWH is preferred if bridging needed 5
• Using LMWH in severe renal failure without dose adjustment – Standard doses carry 2- to 3-fold increased bleeding risk when CrCl <30 mL/min 4, 6
• Discontinuing aspirin when starting heparin in ACS – The combination is intentional and evidence-based; heparin is never used as sole therapy in acute coronary syndromes 5
• Using graduated compression stockings as primary prophylaxis – Not effective and causes lower-extremity skin damage; heparin is superior 3

LMWH vs Unfractionated Heparin

LMWH is superior to UFH for VTE treatment, with significant reductions in mortality and major bleeding during initial therapy 3

Advantages of LMWH:

• No routine laboratory monitoring required (except in renal insufficiency or extreme obesity) 4, 6
• Once or twice daily subcutaneous dosing vs continuous IV infusion 3
• Lower risk of heparin-induced thrombocytopenia (1 case per 1,900 vs 7 per 1,900 with UFH, P=0.07) 3
• Cost-effective or cost-saving compared to UFH 3
• Reduced DVT risk (OR 0.77) and major bleeding (OR 0.43) compared to UFH 8

When UFH is preferred over LMWH:

• Hemodynamic instability requiring rapid reversal capability 4
• Severe renal insufficiency (CrCl <30 mL/min) 4, 6
• Situations requiring immediate anticoagulation with short half-life 2