Key Points
- Use the highest‑yield diagnostic test early; do not let testing delay time‑critical therapy.
- Set objective targets and reassess frequently.
- Plan definitive source control or disease‑specific therapy when indicated; document follow‑up and patient education.
Algorithm
- Stop all heparin; calculate 4T score.
- If intermediate/high → start non-heparin anticoagulant; send PF4 ELISA ± functional assay.
- Confirm diagnosis; transition to oral anticoagulant; document allergy and educate patient.
Clinical Synopsis & Reasoning
Suspect HIT with platelet fall 5–10 days after heparin exposure or sooner with prior exposure. Stop all heparin immediately, estimate probability with the 4T score, send PF4 ELISA and functional assay, and start a non-heparin anticoagulant while awaiting results in intermediate/high probability.
Treatment Strategy & Disposition
Stabilize ABCs. Initiate guideline‑concordant first‑line therapy with precise dosing and continuous monitoring. Escalate to advanced/procedural interventions based on explicit failure criteria. Define ICU, step‑down, and ward disposition triggers; involve specialty teams early.
Epidemiology / Risk Factors
- Risk varies by comorbidity and precipitants; see citations for condition‑specific data.
Investigations
| Test | Role / Rationale | Typical Findings | Notes |
|---|---|---|---|
| 4T score calculation | Pretest probability | Low vs intermediate/high probability | Guides testing/treatment |
| PF4/heparin ELISA ± serotonin release assay | Diagnosis | Confirmatory testing | Interpret with clinical context |
| Duplex ultrasound (if symptoms) | Complications | Occult thrombosis | Screen selectively |
High-Risk & Disposition Triggers
| Trigger | Why it matters | Action |
|---|---|---|
| 4T ≥6 with thrombosis | High risk HIT | Stop heparin; start non-heparin anticoagulant |
| Platelets <30k or bleeding | Bleed risk | Heme consult; careful balance |
Pharmacology
| Medication/Intervention | Mechanism | Onset | Role in Therapy | Limitations |
|---|---|---|---|---|
| Argatroban or Bivalirudin infusion | Direct thrombin inhibitors | Minutes | Immediate anticoagulation | Dose-adjust for organ dysfunction |
| Fondaparinux or DOACs (selected) | Factor Xa inhibition | Hours | Outpatient/step-down therapy | Avoid in renal failure (fondaparinux) |
| Avoid platelet transfusion unless bleeding | Safety | Thrombosis risk | Hematology input |
Prognosis / Complications
- Outcome depends on timeliness of diagnosis and definitive therapy; monitor for complications.
Patient Education / Counseling
- Provide red‑flag education, adherence guidance, and explicit return precautions; arrange timely specialty follow‑up.
References
- ASH guideline on HIT — Link
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