What are the contraindications for heparin use in patients with various medical conditions, including active bleeding, thrombocytopenia, hypertension, renal impairment, hepatic impairment, and those taking medications like aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs)?

Contraindications for Heparin Use

Heparin is absolutely contraindicated in patients with a history of heparin-induced thrombocytopenia (HIT), severe thrombocytopenia, uncontrolled active bleeding (except in disseminated intravascular coagulation), and known hypersensitivity to heparin or pork products. 1

Absolute Contraindications

The FDA-approved labeling identifies four absolute contraindications for heparin use 1:

• History of heparin-induced thrombocytopenia (HIT) or HIT with thrombosis (HITT) – This is the most critical contraindication, as re-exposure can trigger rapid-onset thrombocytopenia and life-threatening thrombotic complications within hours to days 1, 2

• Known hypersensitivity to heparin or pork products – Including anaphylactoid reactions 1

• Uncontrolled active bleeding – Except when due to disseminated intravascular coagulation 1, 2

• Inability to perform appropriate coagulation monitoring – This applies only to full-dose heparin therapy, not low-dose prophylaxis 1

Severe Thrombocytopenia

Heparin should not be used in patients with severe thrombocytopenia, defined as platelet count <50,000/μL for therapeutic dosing. 2, 3

• Discontinue all anticoagulation immediately when platelets fall below 25,000/μL 3
• Between 25,000-50,000/μL, reduce to 50% therapeutic dose or switch to prophylactic dosing only 3
• Full therapeutic anticoagulation is safe only when platelets are ≥50,000/μL 3
• Any degree of thrombocytopenia requires active monitoring for potential HIT development 2, 3

Conditions Requiring Extreme Caution

Low molecular weight heparins (including enoxaparin, tinzaparin, dalteparin) and unfractionated heparin should be used with extreme caution in 2:

• Liver failure with elevated INR >1.5 2
• Uncontrolled arterial hypertension (systolic >200 mmHg or diastolic >110 mmHg) 2
• Severe renal impairment – Particularly important for LMWH, which are renally cleared; patients ≥90 years with creatinine clearance <60 mL/min should not receive tinzaparin 2
• Conditions associated with increased hemorrhage risk – Including bacterial endocarditis, congenital or acquired bleeding disorders, active ulcerative disease 2

Drug Interactions Increasing Bleeding Risk

Concurrent use of antiplatelet agents significantly increases bleeding risk and requires dose reduction of either heparin or the antiplatelet agent. 1

Drugs requiring caution with heparin include 1:

• NSAIDs (aspirin, ibuprofen, indomethacin, celecoxib)
• Thienopyridines (clopidogrel, prasugrel)
• Glycoprotein IIb/IIIa antagonists (abciximab, eptifibatide, tirofiban)
• Dipyridamole, hydroxychloroquine, dextran

These agents interfere with platelet aggregation, which is the main hemostatic defense in heparinized patients 1. The FDA label explicitly recommends dose reduction of antiplatelet agents or heparin when used concomitantly 1.

Special Considerations for HIT History

Patients with documented HIT antibodies still present should receive non-heparin anticoagulants rather than any heparin product. 2

The approach depends on antibody status 2:

• If HIT antibodies are absent (negative ELISA and negative platelet activation assay): Short-term heparin re-exposure may be considered for cardiac surgery only, with strict avoidance of all other heparin exposure pre- and postoperatively 2

• If HIT antibodies are still present: Use non-heparin anticoagulants (bivalirudin, argatroban, danaparoid) rather than any heparin product 2

• Subacute HIT (<3 months): Heparin re-exposure carries significant risk of recurrent thrombocytopenia or thrombosis and should generally be avoided 2

Age and Gender Considerations

• Women have approximately twice the risk of developing HIT compared to men 2
• Patients over 60 years, particularly women, have higher incidence of bleeding complications with heparin therapy 2

Common Pitfalls to Avoid

• Never assume thrombocytopenia is unrelated to heparin – Always calculate a 4Ts score and investigate for HIT when platelets drop ≥30-50% from baseline, even if nadir remains >150,000/μL 2, 3

• Never give platelet transfusions in suspected or confirmed HIT unless there is active life-threatening bleeding – Platelet transfusions paradoxically increase thrombotic risk 2, 4

• Do not start warfarin before platelet count recovery in patients with HIT – This can precipitate venous limb gangrene 2

• Avoid all heparin products in HIT – This includes heparin flushes, catheter locks, and LMWH, as cross-reactivity occurs in 80-100% of cases 5, 6