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cardio.dvt.heparin-induced-thrombocytopenia.v1

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

cardiologyacuteadultacuteinpatienttransitionoutpatient
Start encounter →Print handoutPRODUCTION

Phase E variant of cardio.dvt.core.v1 — narrowed to DVT/VTE in the setting of Heparin-Induced Thrombocytopenia (HIT/HITT). Inherits diagnostic arc and DOAC chronic regimen from parent via routing; specializes for the absolute heparin avoidance pathway, non-heparin parenteral AC selection (argatroban / bivalirudin / fondaparinux / DOAC), and the strict warfarin transition rule (platelets ≥150K + 5-d overlap to avoid venous limb gangrene). Manifest pointer reuses cardio.dvt.core.v1 manifest. Design-brief pointer reuses parent (HIT-specific differences documented inline). Distinguishing features vs generic DVT: (1) heparin (UFH + LMWH + flushes + coated catheters + dialysis circuits) is ABSOLUTELY contraindicated lifelong; (2) thrombocytopenia is the SIDE-EFFECT — thrombosis is the lethal problem (NOT bleeding); (3) 4Ts pretest probability triggers PF4 ELISA + serotonin release assay (gold standard, days to result); (4) treatment is non-heparin AC: argatroban (renal-safe), bivalirudin (peri-procedural), fondaparinux (off-label, evidence supports), or DOAC (apixaban/rivaroxaban — ASH 2018 acceptable in stable patients); (5) warfarin only after platelets ≥150K with 5-day overlap (early warfarin = venous limb gangrene because protein C falls faster than factors II/IX/X); (6) duration ≥3 months for thrombosis; (7) lifelong heparin avoidance education with medical alert bracelet and EHR allergy banner. Status INTEGRATED. Authored 2026-05-15 by shard-06-cardio-acute as HIT/HITT DVT variant.

Entry points (4)

  • lab_abnormality
    ≥50% platelet count drop occurring 5-14 days after starting heparin (UFH or LMWH) — cardinal HIT trigger; 4Ts pretest probability
    platelet_drop_50pct_during_heparin_exposure_day_5_14
  • symptom
    New venous or arterial thrombosis during or shortly after heparin exposure — strong HIT signal even if platelets only mildly down
    new_thrombosis_during_heparin_exposure
  • history
    Rapid-onset thrombocytopenia within hours of heparin exposure in patient with heparin within prior 30 days (re-exposure phenomenon — pre-existing HIT antibodies)
    rapid_onset_thrombocytopenia_with_recent_heparin_exposure_under_30_days
  • imaging
    Limb arterial occlusion, cerebral venous sinus thrombosis, or adrenal vein thrombosis with concurrent thrombocytopenia — pursue HIT workup urgently
    limb_arterial_or_unusual_site_thrombosis_with_thrombocytopenia

Required inputs (12)

  • agerequired
    demographic • used at CONTEXT
    Older patients have higher post-cardiac-surgery HIT incidence (UFH exposure during CPB); age also informs DOAC vs argatroban dose adjustment
  • heparin_exposure_timelinerequired
    history • used at CONTEXT
    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
  • heparin_type_and_routerequired
    history • used at CONTEXT
    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
  • platelet_count_trendrequired
    lab • used at INITIAL_WORKUP
    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)
  • limb_swelling_or_skin_necrosisrequired
    symptom • used at ENTRY
    Cardinal symptom of new thrombosis or warfarin/coumarin skin necrosis; venous limb gangrene if early warfarin overlap
  • compression_usrequired
    imaging • used at INITIAL_WORKUP
    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
  • pf4_heparin_elisarequired
    lab • used at BRANCHING_WORKUP
    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
  • serotonin_release_assayrequired
    lab • used at BRANCHING_WORKUP
    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
  • creatininerequired
    lab • used at TREATMENT
    eGFR for argatroban (no renal adjustment — preferred in renal failure), bivalirudin (renal-adjusted infusion), fondaparinux (avoid CrCl <30), and DOAC dosing
  • lftrequired
    lab • used at TREATMENT
    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
  • inr_ptt_baselinerequired
    lab • used at INITIAL_WORKUP
    Baseline aPTT for argatroban titration target (1.5-3× baseline); baseline INR for warfarin transition planning
  • bleed_riskrequired
    history • used at RED_FLAGS
    HAS-BLED + recent surgery + epidural + ICH history — informs choice and intensity of non-heparin AC; argatroban and bivalirudin are reversible by stopping infusion

12-phase flow (11)

  1. 1FRAME
    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
    inputs: platelet_count_trend
    advance: HIT framed as procoagulant, not bleeding-risk
  2. 2ENTRY
    4Ts pretest probability scoring (Thrombocytopenia, Timing, Thrombosis, oTher cause); compression US to screen for silent DVT; document heparin sources (flushes, dialysis, catheter coatings)
    inputs: heparin_exposure_timeline, heparin_type_and_route, limb_swelling_or_skin_necrosis
    advance: 4Ts score documented and all heparin sources identified
  3. 3CONTEXT
    Cardiac surgery / CPB history (highest HIT risk), recent prior heparin exposure (rapid HIT risk), other thrombocytopenia causes (sepsis, drug, ITP, TMA), bleeding risk, planned procedures
    inputs: age
    advance: context complete
  4. 4RED_FLAGS
    Limb-threatening arterial occlusion, venous limb gangrene (especially if warfarin started early — characteristic), warfarin-induced skin necrosis, cerebral venous sinus thrombosis, adrenal vein thrombosis with adrenal failure, severe TMA differential
    inputs: bleed_risk
    actions: pe_full, thrombocytopenia, acute_limb_ischemia
    advance: critical features screened and all heparin stopped
  5. 5INITIAL_WORKUP
    CBC with platelet trend documented day-by-day; bilateral LE compression US (silent DVT); BMP + LFT + INR/PTT baseline; consider upper-extremity Doppler if catheter site; CT or MR-V for any neuro symptoms
    inputs: compression_us, platelet_count_trend, creatinine, lft, inr_ptt_baseline
    actions: panel.cardiac, panel.renal
    advance: imaging + labs confirm DVT presence/absence
  6. 6BRANCHING_WORKUP
    PF4-heparin ELISA STAT (in-house if available, send-out otherwise — start non-heparin AC empirically while waiting); SRA for ELISA-positive confirmation (gold standard but days to result); rule out other thrombocytopenia causes (sepsis, drug, ITP, TMA — peripheral smear, LDH, haptoglobin, ADAMTS13 if TTP suspected)
    inputs: pf4_heparin_elisa, serotonin_release_assay
    advance: HIT antibody result documented and other causes excluded
  7. 7RISK_STRATIFICATION
    4Ts score + ELISA OD + SRA result interpretation; HAS-BLED for AC bleed risk; eGFR + LFT for non-heparin AC choice; document presence of HITT (HIT with thrombosis — drives ≥3 mo AC duration vs isolated HIT)
    inputs: bleed_risk
    actions: calc.has_bled, calc.ckd_epi_2021
    advance: AC choice + duration plan documented with rationale
  8. 8TREATMENT
    Non-heparin AC immediate. Critically ill / hepatic impairment / unclear NPO status → ARGATROBAN (renal-safe; reduce dose if hepatic dysfunction). Cardiac surgery / catheterisation → BIVALIRUDIN (short half-life, renal-adjusted). Stable inpatient or outpatient → FONDAPARINUX (off-label in HIT, supported by case series and ASH 2018) OR DOAC (apixaban / rivaroxaban — ASH 2018 acceptable in stable patients without progressive thrombosis). Transition to warfarin ONLY AFTER platelets ≥150K with at least 5 days non-heparin AC overlap (avoid early warfarin → venous limb gangrene)
    inputs: creatinine, lft, bleed_risk
    advance: non-heparin AC running, all heparin stopped, warfarin transition criteria documented
  9. 9DISPOSITION
    ICU if HITT + hemodynamic compromise or limb-threatening; cardiology + hematology consult; document EHR allergy/intolerance for HEPARIN (UFH + LMWH + heparin flushes); medical alert bracelet ordered
    advance: unit assigned + allergy banner active in EHR + medical alert bracelet ordered
  10. 10MONITORING
    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
    actions: panel.cardiac
    advance: monitoring schedule documented
  11. 11FOLLOWUP
    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)
    advance: lifelong avoidance education + follow-up + medical alert bracelet documented