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Heparin-Induced Thrombocytopenia

Immune-mediated thrombocytopenia from antibodies to heparin-platelet factor 4 complex with paradoxical thrombosis risk.

Written by: Saygı Hospital Health Guide Editorial Board
Last updated:

This content has been compiled by the Saygı Hospital Health Guide Editorial Board and is periodically reviewed by a specialist physician.

References (5)

This content is for informational purposes only and does not constitute medical advice. You can book an appointment at our Hematoloji department. Book Appointment →

What is Heparin-Induced Thrombocytopenia?

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse reaction to heparin in which IgG antibodies form against the complex of heparin and platelet factor 4 (PF4) released from activated platelets. The IgG-heparin-PF4 immune complexes cross-link platelet FcγRIIa receptors, triggering platelet activation, microparticle release, monocyte and endothelial activation, and a hypercoagulable state. Despite thrombocytopenia, thrombosis (venous or arterial) is the dominant clinical concern.

HIT typically occurs 5-14 days after heparin exposure (immune HIT, type II). Rapid-onset HIT can occur within hours in patients with recent (within 100 days) prior heparin exposure with persistent antibodies. Delayed-onset HIT can present after heparin discontinuation. Type I (non-immune mild thrombocytopenia within first days, transient) is benign and requires no intervention.

Diagnosis uses 4Ts score (thrombocytopenia magnitude, timing, thrombosis or other sequelae, other causes excluded) for pretest probability. Confirmatory testing includes immunoassay (PF4-heparin ELISA) for screening and functional assay (serotonin release assay, heparin-induced platelet activation) for confirmation. Management requires immediate cessation of all heparin (including heparin flushes, LMWH, heparin-coated catheters) and initiation of alternative non-heparin anticoagulant: direct thrombin inhibitor (argatroban, bivalirudin), factor Xa inhibitor (fondaparinux off-label, danaparoid where available), or DOAC (apixaban, rivaroxaban, dabigatran) in stable cases. Warfarin is contraindicated until platelet count recovers (>150,000) due to risk of warfarin-induced limb gangrene from protein C depletion. Duration of anticoagulation depends on thrombosis: at least 4-6 weeks if isolated HIT without thrombosis, 3 months or longer if HIT with thrombosis (HITT).

Symptoms

Platelet count drop 30-50% from baseline 5-14 days after heparin start
Platelet count <100,000/µL or 50% reduction
Venous thrombosis: deep vein thrombosis, pulmonary embolism, cerebral vein, mesenteric vein
Arterial thrombosis: stroke, myocardial infarction, limb ischemia
Skin necrosis at heparin injection sites
Adrenal hemorrhage (Waterhouse-Friderichsen-like) from adrenal vein thrombosis
Catheter thrombosis
Anaphylactoid reaction after IV heparin bolus (rare)
Limb gangrene if warfarin started without alternative anticoagulant
Cerebral venous thrombosis (rare)
Pulmonary infarction
Acute kidney injury from renal artery or vein thrombosis
Disseminated intravascular coagulation overlap (severe HIT)
Prior heparin exposure within 100 days for rapid-onset
No bleeding typical despite thrombocytopenia

Risk Factors

Unfractionated heparin > LMWH (HIT incidence higher with UFH)
Therapeutic dose > prophylactic
Surgical patient > medical (cardiac and orthopedic surgery especially)
Postoperative day 5-14 of heparin
Female sex
Older age
Prior heparin exposure
Cardiopulmonary bypass
Trauma, ICU heparin exposure
Heparin in catheter flushes, coated lines
ECMO
Genetic predisposition (HLA, FcγRIIa polymorphism)
Pregnancy with heparin (lower risk)
Pediatric ICU heparin
Renal impairment affecting alternative anticoagulant choice

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Platelet count drop ≥30-50% during heparin therapy
  • New thrombosis 5-14 days after heparin
  • Skin necrosis at heparin injection site
  • Cardiac surgery patient with platelet drop and thrombosis
  • ECMO patient with thrombocytopenia
  • Anaphylactoid reaction after IV heparin
  • Cerebral, mesenteric, or limb ischemia in heparinized patient
  • Prior history of HIT planning new procedure

Treatment Methods

01
Calculate 4Ts score: thrombocytopenia (magnitude), timing (5-14 days), thrombosis or other sequelae, other causes
02
Send PF4-heparin ELISA (high sensitivity, lower specificity) and confirmatory functional assay (serotonin release assay)
03
Immediately stop all heparin: IV, SC, LMWH, heparin flushes, heparin-coated devices
04
Start alternative non-heparin anticoagulant immediately: argatroban (preferred in renal impairment), bivalirudin (especially in cardiac procedures), fondaparinux (off-label in stable HIT), danaparoid (where available), or DOAC (apixaban, rivaroxaban, dabigatran) in clinically stable cases
05
Avoid warfarin until platelets recover (>150,000) due to risk of warfarin-induced skin necrosis and limb gangrene from protein C depletion
06
Avoid LMWH (cross-reactivity)
07
Avoid platelet transfusion unless life-threatening bleeding (may worsen thrombosis)
08
Imaging for thrombosis based on clinical findings: lower-extremity Doppler ultrasound; CT angiography for PE, stroke, mesenteric ischemia; abdominal CT for adrenal hemorrhage
09
Monitor platelet count daily until recovery; LDH, fibrinogen, D-dimer
10
Treat thrombosis: continue alternative anticoagulant 3 months minimum; longer if persistent risk
11
Isolated HIT without thrombosis: alternative anticoagulant 4-6 weeks; consider DOAC for outpatient
12
Document HIT in medical record and patient identification (medical alert bracelet)
13
Educate patient on lifelong avoidance of heparin (with caveats about cardiac surgery exceptions in distant remote HIT)
14
Cardiac surgery with prior HIT history: testing for residual antibodies; if negative, brief intraoperative heparin acceptable; otherwise bivalirudin
15
Pregnancy: fondaparinux or danaparoid; argatroban or bivalirudin in selected cases; multidisciplinary care
16
ECMO HIT: argatroban or bivalirudin
17
Long-term follow-up: platelet count normalization, anticoagulant duration, thrombosis monitoring
18
Post-HIT: future heparin generally avoided; if essential (e.g. cardiac surgery >100 days from HIT with negative antibody) use brief intraoperative heparin only with hematology consult
19
Multidisciplinary care: hematology, cardiology, vascular surgery, ICU
20
Genetic and immunology workup not routine; HIT typically not recurrent
21
Patient education on bleeding precautions, drug interactions, follow-up schedule

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