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cardio.dvt.heparin-induced-thrombocytopenia.v1PRODUCTION
cardio.dvt.heparin-induced-thrombocytopenia.v1

DVT/VTE with Heparin-Induced Thrombocytopenia (HIT/HITT)

cardiologyacuteadult
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Detailed

HIT = IgG vs PF4-heparin → platelet activation → procoagulant state with thrombocytopenia AND thrombosis; thrombosis (NOT bleeding) is the lethal complication. STOP all heparin (UFH + LMWH + flushes + coated catheters) and start non-heparin AC empirically while awaiting ELISA + SRA

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HIT framed as procoagulant, not bleeding-risk

Patient inputs (12)

PF4-heparin ELISA — high sensitivity (~99%) but moderate specificity; high optical density (OD >1.0 or >2.0) increases positive predictive value; intermediate-high 4Ts → ELISA mandatory

SRA — functional confirmatory assay; gold standard but send-out, days to result; use for ELISA-positive cases needing confirmation; positive SRA = clinically significant HIT antibody

Older patients have higher post-cardiac-surgery HIT incidence (UFH exposure during CPB); age also informs DOAC vs argatroban dose adjustment

Timing of platelet fall vs heparin start: typical HIT 5-14 d post-exposure; rapid HIT (within hours) if recent prior heparin within 30 d; delayed-onset HIT (after stopping heparin) — drives 4Ts Timing component

UFH vs LMWH (LMWH lower HIT incidence ~0.2% vs UFH 1-3%); IV vs SC; heparin flushes; heparin-coated catheter; CPB exposure — drives risk and informs lifelong avoidance education

Cardinal symptom of new thrombosis or warfarin/coumarin skin necrosis; venous limb gangrene if early warfarin overlap

Document baseline pre-heparin platelet, nadir, percent fall, and timing — central to 4Ts Thrombocytopenia component (≥50% fall = 2 points; nadir 20-100K with <30% fall = 1 point)

Bilateral lower extremity compression US to screen for asymptomatic DVT in HIT — silent thrombosis is common; imaging upgrades 4Ts Thrombosis from 1 to 2 points

Baseline aPTT for argatroban titration target (1.5-3× baseline); baseline INR for warfarin transition planning

HAS-BLED + recent surgery + epidural + ICH history — informs choice and intensity of non-heparin AC; argatroban and bivalirudin are reversible by stopping infusion

eGFR for argatroban (no renal adjustment — preferred in renal failure), bivalirudin (renal-adjusted infusion), fondaparinux (avoid CrCl <30), and DOAC dosing

LFT — argatroban requires hepatic dose reduction (start 0.5 mcg/kg/min if hepatic impairment vs 2 mcg/kg/min standard); affects choice of agent in critically ill patient with multi-organ failure

* = hard-required. Engine cannot meaningfully run until these are filled.

Severity triggers (4)

4 need judgement
  • informationallife_threateningvenous_limb_gangrene_from_early_warfarin_overlap
    HIT patient inadvertently started on warfarin before platelet recovery (≥150K) — develops venous limb gangrene within days because warfarin precipitously drops protein C while procoagulant state persists
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningrecurrent_or_progressive_thrombosis_on_argatroban_or_bivalirudin
    HIT patient on therapeutic argatroban or bivalirudin develops new thrombosis or extension despite confirmed therapeutic aPTT — reassess diagnosis (concurrent APS, TTP, malignancy) and consider IVIG or plasma exchange
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateninginadvertent_heparin_re_exposure_after_documented_hit_history
    Patient with documented HIT history receives inadvertent heparin (UFH bolus, LMWH, heparin flush, heparin-coated catheter, dialysis circuit) — lifelong-avoidance education or system safeguards failed
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationalseverepf4_elisa_intermediate_with_negative_sra_result_timeline
    PF4 ELISA returns intermediate optical density (OD 0.4-1.0) with SRA pending or negative — clinical decision-making while awaiting confirmation; continue empiric non-heparin AC if 4Ts intermediate-high; do NOT restart heparin
    Trigger could not be auto-evaluated — needs clinician judgement.

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Recommended regimen

Heparin-induced thrombocytopenia — STOP all heparin, non-heparin AC immediate, warfarin only after platelet recovery (ASH 2018; ACCP 2021)
axis: hit_non_heparin_anticoagulation_with_strict_warfarin_overlap
Selected axis "Heparin-induced thrombocytopenia — STOP all heparin, non-heparin AC immediate, warfarin only after platelet recovery (ASH 2018; ACCP 2021)" by default fallback (first axis)
  • argatroban
    first line
    direct_thrombin_inhibitor
    2 mcg/kg/min IV (start 0.5 mcg/kg/min if hepatic impairment, multi-organ failure, or post-cardiac-surgery); titrate to aPTT 1.5-3× baseline (max 10 mcg/kg/min) • IV • continuous infusion
    triggers: confirmed_or_suspected_hit, hepatic_function_acceptable, critical_illness_or_renal_failure
    ASH 2018 (Cuker PMID 29914917); ACCP 2021 — first-line in critically ill, renal failure (no renal dose adjustment); short half-life ~45 min; reversal by stopping infusion
    rxcui 15202
  • bivalirudin
    first line
    direct_thrombin_inhibitor
    0.15 mg/kg/h IV (renal-adjusted: CrCl 30-60 → 0.1 mg/kg/h; CrCl <30 or HD → 0.05 mg/kg/h); titrate to aPTT 1.5-2.5× baseline • IV • continuous infusion
    triggers: hit_during_pci_or_cardiac_surgery, argatroban_unavailable, hepatic_impairment_severe
    ASH 2018; bivalirudin half-life ~25 min; useful for short procedures (PCI, CPB) and in hepatic dysfunction; renal adjustment required
    rxcui 60819
  • fondaparinux
    first line
    factor_xa_inhibitor_synthetic
    7.5 mg SC daily (5 mg if <50 kg; 10 mg if >100 kg) • SC • daily
    triggers: stable_inpatient_hit, no_renal_failure, no_active_progressive_thrombosis
    ASH 2018 — fondaparinux acceptable for HIT (off-label but evidence supports); does not cross-react with HIT antibodies in vivo (OASIS-5 background, Yusuf NEJM 2006); avoid CrCl <30; no antidote
    rxcui 321208
  • apixaban
    first line
    doac_factor_xa_direct
    10 mg BID × 7 d → 5 mg BID • PO • BID ≥3 months for thrombosis
    triggers: stable_hit_clinically_improving, no_progressive_thrombosis, oral_intake_intact, egfr_above_25
    ASH 2018 — DOAC acceptable in stable HIT patients; ARC consensus 2020 (Cuker Blood Adv 2020); Linkins 2016 cohort + observational data; especially useful for transition from parenteral non-heparin AC and outpatient management
    rxcui 1364430
  • rivaroxaban
    first line
    doac_factor_xa_direct
    15 mg BID × 21 d → 20 mg daily • PO • BID then daily ≥3 months
    triggers: doac_alternative, stable_hit, egfr_above_30
    ASH 2018; alternative DOAC for stable HIT
    rxcui 1114195
  • warfarin
    second line
    vitamin_k_antagonist
    5 mg PO daily; ONLY START after platelets recover ≥150K and overlap ≥5 d with non-heparin AC; INR target 2-3 • PO • daily ≥3 months
    triggers: platelet_recovery_above_150k_after_5d_overlap, long_term_oral_AC_chosen_over_doac
    ASH 2018 — DO NOT start warfarin until platelets ≥150K and after 5-d non-heparin AC overlap; early warfarin precipitates VENOUS LIMB GANGRENE because protein C falls faster than factors II/IX/X; if warfarin started inadvertently before platelet recovery → reverse with vitamin K 5-10 mg PO/IV and continue non-heparin AC
    rxcui 11289
  • vitamin_k_phytonadione
    rescue
    vitamin_k_antidote
    5-10 mg PO or IV • PO or IV • one-time
    triggers: warfarin_started_before_platelet_recovery_in_hit, venous_limb_gangrene_emerging
    ASH 2018 — reverse early-overlap warfarin if HIT diagnosed after warfarin started; restore protein C activity to abort venous limb gangrene
    rxcui 8308

outpatient playbook — drug actions (2)

  1. 1. maintenance apixaban or warfarin
    rxcui 1364430
    apixaban 5 mg BID OR 2.5 mg BID extended-reduced after 6 mo OR warfarin INR 2-3 • PO • BID or daily
    trigger: Per 3-mo decision
    AMPLIFY-EXT (Agnelli NEJM 2013 PMID 23216615); ACCP 2021
  2. 2. pre-procedure non-heparin bridge if indefinite AC
    rxcui 321208
    fondaparinux 2.5 mg SC daily prophylaxis or 7.5 mg SC daily therapeutic; or argatroban infusion if hospitalised • SC or IV • daily or continuous
    trigger: Procedure requiring AC bridging; HEPARIN MUST NOT be used
    ASH 2018 — fondaparinux preferred outpatient bridge in HIT history

Auto-drafted A&P note

outpatient

Subjective

- Possible entry pathways: ≥50% platelet count drop occurring 5-14 days after starting heparin (UFH or LMWH) — cardinal HIT trigger; 4Ts pretest probability; New venous or arterial thrombosis during or shortly after heparin exposure — strong HIT signal even if platelets only mildly down; Rapid-onset thrombocytopenia within hours of heparin exposure in patient with heparin within prior 30 days (re-exposure phenomenon — pre-existing HIT antibodies).

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**DVT/VTE with Heparin-Induced Thrombocytopenia (HIT/HITT)** (cardio.dvt.heparin-induced-thrombocytopenia.v1).
Scope: HIT = IgG vs PF4-heparin → platelet activation → procoagulant state with thrombocytopenia AND thrombosis; thrombosis (NOT bleeding) is the lethal complication. STOP all heparin (UFH + LMWH + flushes + coated catheters) and start non-heparin AC empirically while awaiting ELISA + SRA

No severity triggers fired against current inputs.

Plan

Regimen axis: **Heparin-induced thrombocytopenia — STOP all heparin, non-heparin AC immediate, warfarin only after platelet recovery (ASH 2018; ACCP 2021)**.
1. argatroban 2 mcg/kg/min IV (start 0.5 mcg/kg/min if hepatic impairment, multi-organ failure, or post-cardiac-surgery); titrate to aPTT 1.5-3× baseline (max 10 mcg/kg/min) IV continuous infusion (direct_thrombin_inhibitor, first line) — ASH 2018 (Cuker PMID 29914917); ACCP 2021 — first-line in critically ill, renal failure (no renal dose adjustment); short half-life ~45 min; reversal by stopping infusion
2. bivalirudin 0.15 mg/kg/h IV (renal-adjusted: CrCl 30-60 → 0.1 mg/kg/h; CrCl <30 or HD → 0.05 mg/kg/h); titrate to aPTT 1.5-2.5× baseline IV continuous infusion (direct_thrombin_inhibitor, first line) — ASH 2018; bivalirudin half-life ~25 min; useful for short procedures (PCI, CPB) and in hepatic dysfunction; renal adjustment required
3. fondaparinux 7.5 mg SC daily (5 mg if <50 kg; 10 mg if >100 kg) SC daily (factor_xa_inhibitor_synthetic, first line) — ASH 2018 — fondaparinux acceptable for HIT (off-label but evidence supports); does not cross-react with HIT antibodies in vivo (OASIS-5 background, Yusuf NEJM 2006); avoid CrCl <30; no antidote
4. apixaban 10 mg BID × 7 d → 5 mg BID PO BID ≥3 months for thrombosis (doac_factor_xa_direct, first line) — ASH 2018 — DOAC acceptable in stable HIT patients; ARC consensus 2020 (Cuker Blood Adv 2020); Linkins 2016 cohort + observational data; especially useful for transition from parenteral non-heparin AC and outpatient management
5. rivaroxaban 15 mg BID × 21 d → 20 mg daily PO BID then daily ≥3 months (doac_factor_xa_direct, first line) — ASH 2018; alternative DOAC for stable HIT
6. warfarin 5 mg PO daily; ONLY START after platelets recover ≥150K and overlap ≥5 d with non-heparin AC; INR target 2-3 PO daily ≥3 months (vitamin_k_antagonist, second line) — ASH 2018 — DO NOT start warfarin until platelets ≥150K and after 5-d non-heparin AC overlap; early warfarin precipitates VENOUS LIMB GANGRENE because protein C falls faster than factors II/IX/X; if warfarin started inadvertently before platelet recovery → reverse with vitamin K 5-10 mg PO/IV and continue non-heparin AC
7. vitamin_k_phytonadione 5-10 mg PO or IV PO or IV one-time (vitamin_k_antidote, rescue) — ASH 2018 — reverse early-overlap warfarin if HIT diagnosed after warfarin started; restore protein C activity to abort venous limb gangrene

Setting playbook (outpatient) — Long-term management: AC continuation per individual risk; LIFELONG heparin avoidance; medical alert bracelet permanent; pre-procedure planning for any future surgery / dialysis / catheterisation; antibody re-test only if elective re-exposure required
8. maintenance apixaban or warfarin apixaban 5 mg BID OR 2.5 mg BID extended-reduced after 6 mo OR warfarin INR 2-3 PO BID or daily — Per 3-mo decision (AMPLIFY-EXT (Agnelli NEJM 2013 PMID 23216615); ACCP 2021)
9. pre-procedure non-heparin bridge if indefinite AC fondaparinux 2.5 mg SC daily prophylaxis or 7.5 mg SC daily therapeutic; or argatroban infusion if hospitalised SC or IV daily or continuous — Procedure requiring AC bridging; HEPARIN MUST NOT be used (ASH 2018 — fondaparinux preferred outpatient bridge in HIT history)

Non-pharmacologic actions:
- Compression stocking 30-40 mmHg if PTS symptoms
- Pre-procedure heparin avoidance plan documented before any anticipated surgery / dialysis / cath / hospitalisation
- Patient carries written HIT card
- Medical alert bracelet permanent
- Family + patient education repeatedly reinforced

AVOID / contraindication checks:
- Absolute_contraindication_all_heparin_in_hit_including_LMWH_flushes_coated_catheters_dialysis (ASH 2018)
- Warfarin_contraindicated_until_platelets_above_150K_with_5d_non_heparin_AC_overlap_due_to_venous_limb_gangrene_risk (ASH 2018)
- Fondaparinux_avoid_egfr_below_30 (FDA label)
- Doac_avoid_active_bleeding (FDA labels)
- Argatroban_hepatic_dose_reduction_if_hepatic_impairment_or_post_cardiac_surgery (FDA label)
- Bivalirudin_renal_adjustment_required (FDA label)
- Decision:lifelong_heparin_avoidance_post_hit_including_LMWH (ASH 2018; Warkentin)
- Decision:medical_alert_bracelet_for_heparin_allergy (ASH 2018)
- Decision:ehr_allergy_banner_for_heparin_UFH_LMWH_flushes (institutional safety practice)
- Decision:duration_AC_at_least_3_mo_for_thrombosis_indefinite_if_ongoing_risk (ASH 2018; ACCP 2021)
- Decision:future_cardiac_surgery_repeat_pf4_at_100d_to_assess_antibody_clearance_for_brief_re_exposure (Warkentin)

Monitoring

Regimen monitoring:
- daily platelet count until above 150k stable (ASH 2018)
- aptt q4 6h on argatroban target 1.5 3x baseline (FDA label)
- aptt q4 6h on bivalirudin target 1.5 2.5x baseline (FDA label)
- inr daily during warfarin overlap do not stop argatroban until inr above 4 then recheck inr 4 6h after stopping (ASH 2018)
- cbc creatinine at 4 weeks then quarterly during indefinite AC (FDA labels)
- pts villalta at 3 6 12mo (Kahn Lancet 2014)
- annual AC continuation decision with HASBLED reassessment if indefinite (ACCP 2021)
- pf4 re test at 100d only if elective re exposure to heparin anticipated (Warkentin)
- medical alert bracelet review at every visit (ASH 2018)

Setting (outpatient) monitoring:
- Annual labs + clinical reassessment
- Annual PTS Villalta
- Annual HAS-BLED

Follow-up plan: Hematology long-term follow-up; ≥3 mo AC for thrombosis (longer if ongoing risk); LIFELONG heparin avoidance education (UFH + LMWH including bridging) — medical alert bracelet permanent; future cardiac surgery exposure plan (antibody re-testing at 100 d if elective surgery requires CPB)
- Close-out criterion: lifelong avoidance education + follow-up + medical alert bracelet documented

Monitoring phase: Daily platelet count until ≥150K stable; aPTT q4-6h on argatroban (target 1.5-3× baseline); INR daily once warfarin started — DO NOT stop argatroban until INR ≥4 on overlap then re-check INR 4-6 h after stopping argatroban; PTS Villalta at 3/6/12 mo; bleed surveillance

Disposition

Current setting: outpatient — Long-term management: AC continuation per individual risk; LIFELONG heparin avoidance; medical alert bracelet permanent; pre-procedure planning for any future surgery / dialysis / catheterisation; antibody re-test only if elective re-exposure required

Disposition criteria:
- Indefinite annual follow-up; lifelong avoidance documented across all healthcare systems

Escalation triggers (move to higher acuity):
- New VTE despite AC → reassess adherence + AC adequacy + reconsider switch (DOAC ↔ warfarin)
- Inadvertent heparin re-exposure → STAT PF4 ELISA + clinical observation
- Pregnancy → AC switch (warfarin teratogenic; DOAC not safe in pregnancy; danaparoid or fondaparinux SC for AC in pregnancy with HIT history per ASH 2018 pregnancy)
- Major bleed → reverse, hold, reassess indefinite indication

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] HIT patient inadvertently started on warfarin before platelet recovery (≥150K) — develops venous limb gangrene within days because warfarin precipitously drops protein C while procoagulant state persists
- [LIFE_THREATENING] HIT patient on therapeutic argatroban or bivalirudin develops new thrombosis or extension despite confirmed therapeutic aPTT — reassess diagnosis (concurrent APS, TTP, malignancy) and consider IVIG or plasma exchange
- [LIFE_THREATENING] Patient with documented HIT history receives inadvertent heparin (UFH bolus, LMWH, heparin flush, heparin-coated catheter, dialysis circuit) — lifelong-avoidance education or system safeguards failed

Citations

- ASH 2018 Heparin-Induced Thrombocytopenia (Cuker) + ACCP/CHEST 2021 (Stevens) for AC duration [PMID:29914917](https://pubmed.ncbi.nlm.nih.gov/29914917/)
- Cited evidence (PMID 34352295) [PMID:34352295](https://pubmed.ncbi.nlm.nih.gov/34352295/)
- Cited evidence (PMID 33007077) [PMID:33007077](https://pubmed.ncbi.nlm.nih.gov/33007077/)
- Cited evidence (PMID 26222563) [PMID:26222563](https://pubmed.ncbi.nlm.nih.gov/26222563/)
- Cited evidence (PMID 16634744) [PMID:16634744](https://pubmed.ncbi.nlm.nih.gov/16634744/)

Last reconciled with current guidelines: 2026-05-15.
References