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Heparin-Induced Thrombocytopenia (HIT)
Cardiovascular Presentations
Abdominal aortic aneurysm
Acute coronary syndrome (NSTEMI)
Acute coronary syndrome (STEMI)
Acute decompensated heart failure
Acute limb ischemia
Acute mesenteric ischemia
Aortic dissection
Aortic stenosis
Atrial fibrillation and flutter
Bradyarrhythmia and heart block
Cardiac arrest
Deep vein thrombosis
Myocarditis
Pericarditis
Pulmonary embolism
Stable angina
Superficial thrombophlebitis
Superior vena cava syndrome
Supraventricular tachycardia
Syncope (cardiogenic)
Unstable angina
Ventricular tachycardia
Respiratory Presentations
Acute bronchitis
Acute respiratory failure
Aspiration pneumonia
Asthma exacerbation
Bronchiolitis
Community-acquired pneumonia
COVID-19 pneumonia
COPD exacerbation
Croup
Croup (laryngotracheobronchitis)
Epiglottitis
Hemothorax
Hospital-acquired pneumonia
Pleural effusion
Pneumothorax (traumatic)
Pulmonary contusion
Spontaneous pneumothorax
Neurological Presentations
Bell's palsy
Benign paroxysmal positional vertigo
Brain abscess
Cauda equina syndrome
Cervical radiculopathy
Concussion (mild traumatic brain injury)
Encephalitis
Guillain-Barré syndrome
Hemorrhagic stroke (intracerebral)
Ischemic stroke
Lumbar radiculopathy
Malignant spinal cord compression
Migraine
Peripheral neuropathy (acute)
Retropharyngeal abscess
Schizophrenia (acute exacerbation)
Seizure (breakthrough:known epilepsy)
Seizure (first-time)
Spinal cord injury
Status epilepticus
Subarachnoid hemorrhage
Tension headache
Transient ischemic attack
Traumatic brain injury (moderate-severe)
Vestibular neuritis
Viral meningitis
Gastrointestinal Presentations
Acute appendicitis
Acute cholecystitis
Acute diverticulitis
Acute pancreatitis
Anal fissure
Choledocholithiasis and cholangitis
Clostridioides difficile colitis
Gastritis
Gastroenteritis (viral and bacterial)
Gastroesophageal reflux disease
Incarcerated or strangulated hernia
Inflammatory bowel disease flare
Large bowel obstruction
Lower GI hemorrhage
Peptic ulcer disease
Perforated viscus
Small bowel obstruction
Upper GI hemorrhage
Genitourinary and Reproductive Presentations
Acute prostatitis
Acute urinary retention
Ectopic pregnancy
Epididymitis
Orchitis
Ovarian torsion
Paraphimosis
Pelvic inflammatory disease
Priapism
Pyelonephritis
Renal laceration
Ruptured ovarian cyst
Testicular torsion
Tubo-ovarian abscess
Urinary tract infection (uncomplicated)
Urolithiasis (renal colic)
Vaginal bleeding (non-pregnant)
Infectious Disease Presentations
Acute sinusitis
Acute tonsillitis
Acute upper respiratory infection
Animal bite
Bacterial meningitis
Cellulitis
Conjunctivitis (bacterial)
Dental abscess
Endocarditis
Febrile neutropenia
Fournier gangrene
Hand-foot-mouth disease
Hepatitis (acute)
Herpes zoster
HIV-related illness
Human bite
Impetigo
Infected diabetic foot ulcer
Infectious mononucleosis
Influenza
Necrotizing fasciitis
Osteomyelitis
Otitis externa
Parasitic infection
Periorbital cellulitis
Peritonsillar abscess
Scabies
Sepsis
Septic arthritis
Spontaneous bacterial peritonitis
Tick-borne illness (Lyme disease)
Tinea infection
Tuberculosis
Viral exanthem
Wound infection
Trauma Presentations
Achilles tendon rupture
ACL and mceniscus tear
Ankle fracture
Ankle sprain
Burn
Calcaneus fracture
Cervical spine fracture
Clavicle fracture
Dental avulsion
Distal radius fracture
Drowning
Elbow fracture and dislocation
Electrical injury
Facial bone fracture
Facial laceration
Femur fracture
Fingertip amputation
Forearm fracture (radius and ulna)
Frostbite
Hand:finger laceration
Heat exhaustion
Heat stroke
Hip fracture
Humeral shaft fracture
Knee dislocation
Knee sprain
Lightning injury
Mandible fracture
Metacarpal fracture
Metatarsal fracture
Muscle strain
Nasal fracture
Non-accidental trauma
Orbital fracture
Patella fracture
Phalanx fracture (finger)
Proximal humerus fracture
Pulmonary contusion
Rib fracture
Rotator cuff tear (acute traumatic)
Scalp laceration
Scaphoid fracture
Shoulder dislocation
Skull fracture
Splenic laceration
Sternal fracture
Supracondylar pediatric fracture
Tendon laceration (hand:wrist)
Thoracic and lumbar spine fracture
Tibia:fibula fracture
Tibial plateau fracture
Toe fracture
Traumatic epistaxis
Traumatic hyphema
Toxicologic Presentations
Acetaminophen toxicity
Alcohol intoxication
Alcohol withdrawal
Anticholinergic toxicity
Anticoagulant overdose
Benzodiazepine overdose
Benzodiazepine:sedative overdose
Beta-blocker and calcium channel blocker toxicity
Carbon monoxide poisoning
Caustic ingestion
Digoxin toxicity
Drug eruption
Foreign body ingestion
Opioid intoxication
Opioid overdose
Opioid withdrawal
Organophosphate
Salicylate toxicity
Serotonin syndrome
Stimulant intoxication (cocaine, methamphetamine)
Tricyclic antidepressant overdose
Psychiatric Presentations
Acute anxiety
Acute psychosis
Agitation:behavioral emergency
Bipolar disorder
Conversion disorder
Major depressive episode
Neuroleptic malignant syndrome
Suicidal ideation and attempt
Musculoskeletal and Rheumatologic Presentations
Acute low back pain (mechanical)
Bursitis
Cervical radiculopathy
Costochondritis
Gout (acute)
Lumbar radiculopathy
Pseudogout
Tendinitis
Dermatology Presentations
Acute eczema (Eczema acute flare)
Allergic contact dermatitis
Erythema multiforme
Henoch-Schönlein purpura
Pressure injury
Psoriasis (acute flare)
Stevens-Johnson syndrome
Toxic epidermal necrolysis
Urticaria (acute)
Environmental and Exposure Presentations
Envenomation (snake, spider, insect)
High-altitude illness
Hypothermia
Hematologic and Oncologic Presentations
Acute chest syndrome
Coagulopathy
Hyperviscosity syndrome
Sickle cell crisis (vaso-occlusive)
Symptomatic anemia
Thrombocytopenia (severe)
Tumor lysis syndrome
Pediatric-Specific Presentations
Bronchiolitis
Croup
Emergency delivery
Febrile seizure
Kawasaki disease
Neonatal jaundice
Neonatal sepsis
Nursemaid's elbow
Pediatric fever 0 to 28 days
Pediatric fever 29 to 60 days
Pediatric fever 61 to 90 days
Pyloric stenosis
Slipped capital femoral epiphysis
Intussusception
Endocrine and Metabolic Presentations
Adrenal crisis
Diabetic ketoacidosis
Hypercalcemia
Hyperosmolar hyperglycemic state
Hypertensive emergency
Hypertensive urgency
Hypoglycemia
Myasthenia gravis crisis
Myxedema coma
Severe hyperkalemia
Severe hyponatremia
Thyroid storm
ENT and Maxillofacial Presentations
Acute laryngitis
Acute otitis media
Acute pharyngitis
Cerumen impaction
Epistaxis (anterior)
Nasal foreign body
Otitis externa
Tympanic membrane perforation
Ophthalmologic Presentations
Acute angle-closure glaucoma
Central retinal artery occlusion
Chemical eye injury
Corneal abrasion
Corneal ulcer
Globe rupture
Ocular foreign body
Orbital cellulitis
Retinal detachment
Obstetric Presentations
Hyperemesis gravidarum
Painful vaginal bleeding in pregnancy
Placenta previa
Placental abruption
Preeclampsia:eclampsia
Preterm labor
Threatened:inevitable:incomplete abortion
Systemic and Miscellaneous Presentations
Anaphylaxis
Angioedema
Cannabis-induced hyperemesis
Heparin-Induced Thrombocytopenia (HIT)
POCUS
Procedures
Calculators
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ECG Guide
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Clinical Assessment Checklist
Browse categories and answer follow-up questions to refine your symptom profile.
Approach to the Critical Patient
Immediate priorities
HIT recognition triggers
▶
Platelet count drop >50% from baseline in heparin-exposed patient
▶
Even if absolute count remains above 100 x10^9/L
Nadir rarely below 20 x10^9/L in typical HIT
New thrombosis concurrent with thrombocytopenia
▶
DVT, PE, arterial occlusion, stroke, mesenteric ischemia
Thrombosis occurs in approximately 50% of untreated confirmed cases
Acute systemic reaction after IV heparin bolus
▶
Fever, chills, tachycardia, hypotension, dyspnea
Suggests rapid-onset HIT from prior sensitization
Skin necrosis at heparin injection sites
▶
Distinctive finding with high specificity for HIT
Associated with subcutaneous heparin administration
Immediate actions
Stop all heparin immediately upon intermediate or high clinical suspicion
▶
Discontinue UFH and LMWH infusions and injections
Discontinue heparin flushes and lock solutions
Replace heparin-coated catheters
Do not wait for laboratory confirmation before stopping heparin
Initiate non-heparin therapeutic anticoagulation
▶
Rate of thrombosis without anticoagulation is approximately 5% per day
Argatroban or bivalirudin as first-line in ICU or hospitalized patients
Start immediately if intermediate or high 4Ts score
Warfarin management
▶
Do not initiate warfarin until platelets recover to >=150 x10^9/L
If already on warfarin, reverse with vitamin K 10 mg IV
▶
Warfarin depletes protein C and worsens prothrombotic state
Risk of warfarin-induced venous limb gangrene
Monitoring and escalation
Hemodynamic monitoring
▶
Continuous cardiac monitoring for tachyarrhythmia from PE
Serial blood pressure for hypotension from massive PE or DIC
Pulse oximetry for PE-related hypoxia
Platelet and lab trajectory
▶
Serial platelet counts every 1 to 2 days until recovery
aPTT monitoring every 4 to 6 hours during DTI infusion
Coagulation panel if DIC suspected
Escalation triggers
▶
Limb ischemia or gangrene — vascular surgery consult immediately
Hemodynamically significant PE — critical care and IR consult
DIC with active bleeding — hematology consult and intensive monitoring
Consult triggers
Specialist activation
▶
Hematology — all confirmed or strongly suspected HIT cases
Vascular surgery — limb ischemia, arterial thrombosis, gangrene
Interventional radiology — catheter-directed thrombolysis for massive DVT or PE
Critical care — hemodynamic instability, DIC, multi-organ failure
History
Heparin exposure profile
Type and route of heparin
▶
UFH carries approximately 10-fold higher risk than LMWH
Line flushes and heparin-coated catheters often overlooked
Dialysis circuits as exposure source
Timing of platelet drop relative to heparin initiation
▶
Classic onset days 5 to 10 after first heparin exposure
Rapid-onset HIT within hours if prior heparin exposure within 30 to 100 days
Delayed-onset HIT presenting after heparin cessation
Duration of current heparin course
▶
Risk increases with more than 5 days of therapy
Surgical patients at higher risk than medical patients
Thrombotic symptom screen
Venous thromboembolism symptoms
▶
Limb swelling, pain, erythema, warmth suggesting DVT
Dyspnea, pleuritic chest pain, hemoptysis suggesting PE
Abdominal pain suggesting mesenteric or splanchnic vein thrombosis
Arterial thrombosis symptoms
▶
Focal neurologic deficits, vision loss, speech difficulty suggesting stroke
Chest pain suggesting myocardial infarction
Absent pulses, cool limb, pain suggesting peripheral arterial occlusion
Abdominal pain with gut ischemia features
Skin findings history
▶
Erythematous lesions at heparin injection sites
Progression to skin necrosis
Occurs in 10% to 20% of HIT cases
Risk factors
Patient-specific risk
▶
Surgical patients 1% to 5% incidence with UFH versus medical patients 0.1% to 1%
Cardiac surgery and post-cardiopulmonary bypass highest risk group
Orthopedic surgery including hip and knee arthroplasty
Female sex approximately twice the risk of male patients
Prior heparin exposure within 100 days increases rapid-onset HIT risk
Prior HIT history
▶
Document clearly in chart — lifelong heparin avoidance generally recommended
Re-exposure only in select cases when antibodies confirmed negative
Recent surgeries resetting the immunologic clock
Alarm features
High-urgency clinical context
▶
New thrombosis in setting of falling platelets on heparin
Acute systemic anaphylactoid reaction after IV heparin bolus
DIC features — fibrinogen depletion, elevated D-dimer, coagulopathy
Thrombocytopenia developing while on warfarin without non-heparin anticoagulant bridge
Absence of petechiae, purpura, or mucosal bleeding despite thrombocytopenia
▶
HIT is prothrombotic not hemorrhagic
Bleeding pattern should raise alternative diagnosis
Important negatives
Features arguing against HIT
▶
Platelet drop within first 48 hours without prior heparin exposure
▶
Suggests non-immune heparin-associated thrombocytopenia (Type I)
Benign and self-limited
Spontaneous mucosal bleeding or petechiae
▶
Unusual in HIT despite thrombocytopenia
Platelet nadir below 20 x10^9/L
▶
More typical of TTP, ITP, or DIC than HIT
Physical Exam
Vital signs
Hemodynamic snapshot
▶
Tachycardia from PE, systemic anaphylactoid reaction, or DIC
Hypotension from massive PE, anaphylactoid reaction, or DIC
Tachypnea and hypoxia from PE or ARDS
Temperature elevation in acute systemic HIT reaction
Extremity and vascular exam
DVT and arterial findings
▶
Unilateral leg swelling, erythema, warmth, tenderness suggesting DVT
Cool, pale, or pulseless limb indicating arterial occlusion
Gangrene in advanced limb ischemia
Upper extremity involvement if central venous catheter present
Skin exam
▶
Necrosis or erythematous plaques at heparin injection sites
Livedo reticularis pattern from microemboli
Notably absent petechiae and purpura despite thrombocytopenia
▶
Absence of mucosal bleeding distinguishes HIT from other thrombocytopenias
Pulmonary exam
PE-related findings
▶
Decreased breath sounds or pleural rub suggesting PE or effusion
Signs of right heart strain in massive PE
Tachypnea with accessory muscle use
Abdominal exam
Visceral thrombosis signs
▶
Diffuse tenderness suggesting mesenteric ischemia
Peritoneal signs if bowel infarction
Hepatosplenomegaly if splanchnic vein thrombosis
Neurologic exam
Cerebrovascular assessment
▶
Focal motor or sensory deficits suggesting stroke
Speech difficulty or dysarthria
Headache with focal deficits suggesting cerebral venous sinus thrombosis
Visual field deficits
PITFALLS
Examination pitfalls
▶
Thrombocytopenia without thrombosis still requires anticoagulation
▶
Isolated HIT has high thrombotic risk without treatment
Do not withhold anticoagulation based on absence of visible thrombosis
Skin necrosis at injection sites misattributed to other causes
▶
Highly specific for HIT when at heparin injection sites
Limb gangrene in warfarin-exposed HIT patient
▶
Warfarin-induced venous limb gangrene if warfarin started without DTI bridge
Differential Diagnosis
Life-threatening diagnoses to exclude
Cannot-miss thrombocytopenia causes
▶
Thrombotic thrombocytopenic purpura (TTP)
▶
ICD-10 M31.1
Schistocytes on peripheral smear, low ADAMTS13 activity
Neurologic and renal involvement, fever
Disseminated intravascular coagulation (DIC)
▶
ICD-10 D65
Elevated D-dimer, low fibrinogen, prolonged PT and aPTT
DIC can coexist with HIT in up to 20% of cases
Vaccine-induced immune thrombocytopenia and thrombosis (VITT)
▶
Similar anti-PF4 mechanism but without heparin exposure
History of recent COVID-19 adenoviral vector vaccine
Common mimics
Benign and less urgent causes
▶
Non-immune heparin-associated thrombocytopenia (HAT Type I)
▶
Mild transient platelet drop within first 2 days of heparin
Non-immune mediated, benign, self-limited
No antibodies, no thrombosis
Sepsis-related thrombocytopenia
▶
ICD-10 D69.59
Positive cultures, clinical sepsis, multiorgan dysfunction
Drug-induced thrombocytopenia
▶
Antibiotics, GPIIb/IIIa inhibitors, chemotherapy, quinine
Temporal relationship with offending drug
Dilutional thrombocytopenia
▶
Massive transfusion or aggressive fluid resuscitation history
Post-surgical hemodilution
Mechanical platelet destruction
▶
IABP, ECMO, ventricular assist devices
Hemolysis evidence on smear
Pseudothrombocytopenia
▶
EDTA-dependent platelet clumping on automated count
Normal count on citrate or heparin tube repeat
Differentiating HIT
Features favoring HIT over mimics
▶
Thrombocytopenia with thrombosis rather than bleeding
Typical onset timing days 5 to 10 after heparin initiation
Platelet nadir rarely below 20 x10^9/L
Positive PF4/heparin ELISA and functional assay
ICD-10 D75.82 heparin-induced thrombocytopenia
Laboratory Tests
Pretest probability — 4Ts score
4Ts clinical scoring components
▶
Thrombocytopenia degree
▶
>50% fall from baseline with nadir >=20: 2 points
30% to 50% fall or nadir 10 to 19: 1 point
<30% fall or nadir <10: 0 points
Timing of platelet fall
▶
Clear onset days 5 to 10 or fall within 1 day with prior heparin within 30 days: 2 points
Consistent with days 5 to 10 but not clear or >10 days or unknown: 1 point
Fall within 4 days without prior heparin exposure: 0 points
Thrombosis or other sequelae
▶
New thrombosis, skin necrosis, or acute systemic reaction: 2 points
Progressive or recurrent thrombosis or erythematous skin lesions: 1 point
None: 0 points
Other causes of thrombocytopenia
▶
None apparent: 2 points
Possible alternative cause: 1 point
Definite alternative cause: 0 points
Score interpretation
▶
Low (0 to 3): HIT unlikely, NPV 97% to 99% with negative ELISA
Intermediate (4 to 5): moderate probability, send ELISA and functional assay
High (6 to 8): high probability, start non-heparin anticoagulation immediately
Immunoassays
PF4/heparin ELISA
▶
High sensitivity 95% to 99% for HIT antibody detection
Moderate specificity — many ELISA-positive patients do not have clinical HIT
Optical density correlates with clinical probability
▶
OD >1.5 to 2.0 correlates with higher likelihood of true HIT
OD <0.4 with low 4Ts effectively excludes HIT
Result turnaround typically 1 to 2 days
Rapid immunoassay
▶
Chemiluminescent immunoassay available at some centres
Faster turnaround for expedited clinical decisions
Functional confirmatory assay
Serotonin release assay (SRA)
▶
Gold standard for confirming platelet-activating HIT antibodies
Specificity >95% for clinical HIT
Detects functional antibody that activates platelets in presence of heparin
Requires specialized laboratory, result may take several days
Heparin-induced platelet activation (HIPA) assay
▶
Alternative functional assay used in some centres
Similar sensitivity and specificity to SRA
P-selectin expression assay
▶
Flow cytometry-based alternative functional assay
Measures platelet activation by patient serum in presence of heparin
Additional laboratory workup
Coagulation and DIC panel
▶
PT, aPTT, fibrinogen, D-dimer for DIC assessment
DIC occurs in up to 20% of HIT patients
Baseline aPTT and INR before starting alternative anticoagulation
▶
HIT itself can elevate aPTT and INR at baseline
Microangiopathy screen
▶
Peripheral blood smear for schistocytes
LDH and haptoglobin to exclude TTP
ADAMTS13 activity if TTP suspected
Organ function and anticoagulant dosing inputs
▶
Creatinine and CrCl for bivalirudin and fondaparinux dosing
Liver function tests for argatroban dosing adjustment
CBC with differential for full platelet trend
Diagnostic Tests
Scoring Systems
4Ts score for pretest probability
▶
Four components scored 0 to 2 each giving maximum score 8
Low score 0 to 3 with negative ELISA: NPV 97% to 99% effectively rules out HIT
Intermediate score 4 to 5: send ELISA and functional assay, manage clinically
High score 6 to 8: start non-heparin anticoagulation before laboratory confirmation
Validated in systematic review and meta-analysis by Cuker et al, Blood 2012
Not validated in cancer patients — alternative causes common, interpret cautiously
HIT Expert Probability (HEP) score
▶
More detailed 8-item score including medication list, bleeding assessment
May improve discrimination over 4Ts in some populations
Less widely adopted than 4Ts in clinical practice
MRI
MRI indications in HIT
▶
Cerebral venous sinus thrombosis (CVST) suspected
▶
MR venography preferred modality for CVST
Non-contrast MRI and MRV identify filling defects
Stroke evaluation when arterial or venous cerebral thrombosis suspected
▶
DWI sequence for acute ischemic infarct
MRA for arterial occlusion
Spinal cord ischemia from arterial thrombosis
▶
T2 signal changes in cord ischemia
Contraindications
▶
Hemodynamically unstable patient requiring monitoring
Non-MRI-compatible implants or devices
CT preferred for initial evaluation in most emergent HIT presentations
CT
CT pulmonary angiography
▶
First-line imaging for suspected PE in HIT
Sensitivity approximately 83% to 100% for PE
Protocol: IV contrast, 100 to 120 kV, ECG-gated optional
Assess for right heart strain on CT
▶
RV to LV ratio >0.9 indicating right heart strain
Contrast reflux into IVC
CT angiography of limbs and abdomen
▶
Arterial thrombosis and limb ischemia evaluation
Mesenteric ischemia and splanchnic vein thrombosis
CT venography for upper extremity DVT evaluation
CT head
▶
Cerebral arterial or venous thrombosis initial evaluation
Non-contrast CT for hemorrhagic transformation before anticoagulation decisions
CT limitations in HIT
▶
Contrast nephropathy risk — assess CrCl before administration
Radiation exposure relevant for recurrent imaging needs
Ultrasound
Lower extremity duplex ultrasound
▶
Recommended for all confirmed HIT patients to screen for asymptomatic DVT
Sensitivity >90% for proximal DVT
Assess bilateral lower extremities even without clinical symptoms
Compression and Doppler assessment of common femoral to popliteal veins
Upper extremity duplex ultrasound
▶
Indicated if central venous catheter present
Subclavian, internal jugular, and axillary vein assessment
DVT highly associated with catheter tip location in HIT
Echocardiography
▶
Right heart strain assessment in PE
Paradoxical embolism through PFO
Intracardiac thrombus from severe PE or catheter-related thrombosis
Abdominal ultrasound
▶
Hepatic and portal vein thrombosis screening
Splenic and mesenteric vein assessment
Limited by bowel gas — CT preferred for mesenteric ischemia
Disposition
Admission criteria
All suspected or confirmed HIT requiring IV anticoagulation
▶
Argatroban or bivalirudin require continuous infusion and aPTT monitoring
Dose titration requires nursing capacity for frequent monitoring
IV anticoagulation cannot be safely managed in an outpatient setting
HIT with thrombosis (HITT)
▶
DVT, PE, arterial thrombosis, stroke, mesenteric ischemia
Limb-threatening ischemia or gangrene
Adrenal hemorrhagic infarction
Hemodynamic instability
▶
Massive or submassive PE with right heart strain
DIC or active bleeding
Multi-organ failure
ICU-level care indications
Critical deterioration criteria
▶
Vasopressor requirement from massive PE or DIC
Mechanical ventilation for PE-related respiratory failure
Active arterial limb ischemia requiring urgent intervention
DIC with coagulopathy and active hemorrhage
Outpatient management considerations
Select stable patients only
▶
Isolated HIT without thrombosis confirmed by specialist assessment
Fondaparinux SC or DOAC initiated and tolerated
Close outpatient monitoring with daily platelet counts available
Hematology follow-up within 24 to 48 hours confirmed before discharge
Specialist consultation prior to disposition
Copy
Hematology consultation for all confirmed or strongly suspected HIT
▶
Anticoagulant selection and duration decision
Outpatient management planning if applicable
Transfer criteria
▶
Limb-threatening ischemia requiring vascular surgical intervention not available locally
Catheter-directed thrombolysis or thrombectomy capability not at receiving facility
Treatment
Stop all heparin
Heparin cessation steps
▶
Discontinue IV UFH infusion immediately
Discontinue SC LMWH injections
Discontinue all heparin flushes and lock solutions
Change to heparin-free catheter management
Switch dialysis circuit to non-heparin anticoagulation
LMWH has approximately 90% cross-reactivity with HIT antibodies — not an alternative
Argatroban
Argatroban direct thrombin inhibitor
▶
Initial infusion rate 2 mcg/kg/min
▶
Reduce to 0.5 mcg/kg/min if hepatic dysfunction or critical illness
ICU patients often require lower starting dose
Monitoring target
▶
aPTT 1.5 to 3 times baseline
First check at 2 hours after initiation
Adjust infusion by 0.5 to 1 mcg/kg/min every 2 hours until target reached
Maximum dose 10 mcg/kg/min
Clearance primarily hepatic
▶
Avoid or reduce dose significantly in hepatic dysfunction
Preferred in renal failure patients
Prolongs INR — complicates warfarin transition
▶
Use chromogenic factor X assay for warfarin monitoring
Target INR approximately 4.0 on argatroban before stopping if switching to warfarin
ACCP Grade 1C recommendation for argatroban in HIT
Bivalirudin
Bivalirudin direct thrombin inhibitor
▶
Initial infusion rate 0.15 mg/kg/h
▶
Reduce dose for renal impairment
CrCl 30 to 60 mL/min: reduce to 0.08 to 0.1 mg/kg/h
CrCl <30 mL/min: reduce to 0.03 to 0.05 mg/kg/h
Monitoring target
▶
aPTT 1.5 to 2.5 times baseline
First check at 2 hours after initiation
Titrate by 0.05 mg/kg/h increments
Clearance 80% enzymatic, 20% renal
▶
Preferred when combined hepatic and renal dysfunction
Anaphylaxis reported rarely
Does not artificially prolong INR as significantly as argatroban
Fondaparinux
Fondaparinux subcutaneous
▶
Weight-based once-daily dosing
▶
<50 kg: 5 mg SC daily
50 to 100 kg: 7.5 mg SC daily
>100 kg: 10 mg SC daily
Avoid if CrCl <30 mL/min — renal elimination
Does not cross-react with HIT antibodies
Useful for patients outside ICU who can tolerate SC injection
No routine monitoring of anti-Xa levels required in most patients
Cannot be reversed by protamine
DOACs for HIT
Direct oral anticoagulants
▶
Rivaroxaban has most supporting data for HIT
▶
15 mg PO twice daily with food for 3 weeks then 20 mg PO daily for VTE treatment
Reasonable for clinically stable patients without hemodynamically significant PE
Apixaban alternative
▶
10 mg PO twice daily for 7 days then 5 mg PO twice daily
DOAC initiation timing
▶
Start at time of DTI discontinuation when clinically stable
Not recommended for acute limb-threatening arterial thrombosis or hemodynamically significant PE
ASH 2018 guidelines conditionally recommend DOACs for non-acute HIT management
Transition to long-term anticoagulation
Warfarin transition
▶
Initiate only when platelets >=150 x10^9/L
Overlap with DTI or fondaparinux for minimum 5 to 7 days
Target INR 2.0 to 3.0 for most indications
If using argatroban as bridge, target INR approximately 4.0 on combined therapy
Chromogenic factor X assay confirms adequate anticoagulation during transition
Duration of anticoagulation
▶
Isolated HIT without thrombosis: minimum 4 weeks; some guidelines recommend up to 3 months
HIT with thrombosis: minimum 3 months
Anticoagulation duration based on thrombosis extent and recurrence risk
Refractory and autoimmune HIT
IVIG for refractory or autoimmune HIT
▶
IVIG 1 g/kg IV daily for 2 days
Inhibits FcgammaRIIA-mediated platelet activation
Consider in autoimmune HIT presenting after heparin cessation
Also consider in HIT with severe thrombocytopenia and ongoing thrombosis on DTI
Platelet transfusion
Platelet transfusion
▶
Avoid platelet transfusions in HIT unless active life-threatening bleeding
Thrombosis risk outweighs benefit in most HIT patients
If transfusion necessary, threshold platelets <50 x10^9/L with active bleeding
ACCP Grade 1C recommendation against routine platelet transfusion in HIT
Surgical and interventional management
Vascular interventions
▶
Catheter-directed thrombolysis for iliofemoral DVT causing phlegmasia
Surgical thromboembolectomy for acute limb ischemia
IVC filter placement generally avoided in HIT — additional thrombogenic risk
If filter required, use non-heparin anticoagulation perioperatively
Special Populations
Pregnancy
Pregnancy-specific HIT management
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Heparin exposure common in pregnancy for VTE prophylaxis and treatment
HIT incidence in pregnancy lower than surgical populations but not negligible
UFH associated with HIT even at prophylactic doses in pregnancy
Anticoagulant selection in pregnancy
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Fondaparinux: limited safety data but used in pregnancy when no alternative
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Crosses placenta in small amounts
Generally considered acceptable when benefits outweigh risks
Argatroban and bivalirudin: limited safety data in pregnancy
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Use only when fondaparinux not appropriate
Hematology and maternal-fetal medicine co-management recommended
DOACs: contraindicated in pregnancy — teratogenic potential
Warfarin: contraindicated in first trimester and near delivery
Monitoring in pregnancy
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Fondaparinux does not require routine anti-Xa monitoring
Renal function monitoring important as GFR changes in pregnancy
Fetal monitoring appropriate based on gestational age
Delivery planning
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Multidisciplinary planning with obstetrics, hematology, and anesthesia
Regional anesthesia timing relative to last anticoagulant dose
Fondaparinux half-life approximately 17 to 21 hours — plan 2 to 3 days before neuraxial
Geriatric
Older adult HIT considerations
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Higher baseline heparin exposure from comorbidities and hospitalizations
Greater renal impairment — adjust bivalirudin and fondaparinux doses
Hepatic dysfunction affects argatroban clearance
Thrombosis risk in older adults
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Higher baseline VTE risk with reduced mobility
Arterial disease comorbidities increase arterial thrombosis impact
Stroke from HIT has worse outcomes in older adults
Anticoagulation safety
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Higher bleeding risk from falls, polypharmacy, and drug interactions
DOAC renal dosing adjustments important in elderly
Avoid fondaparinux if CrCl <30 mL/min — common in older adults
Monitoring adjustments
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aPTT target range same but baseline aPTT may vary
More frequent platelet monitoring given polypharmacy contributions
Pediatrics
Pediatric HIT considerations
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HIT is rare in children but increasingly recognized with growing ECMO and cardiac surgery use
Incidence estimated at 0.3% to 1% in exposed pediatric patients
Cardiac surgery and ECMO highest risk settings in children
Diagnosis in pediatrics
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4Ts score not validated in pediatric population
Clinical suspicion and PF4/ELISA used analogously to adults
Platelet drop thresholds apply similarly
Anticoagulant dosing in children
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Argatroban: 0.75 mcg/kg/min initial dose in children; titrate to aPTT 1.5 to 3 times baseline
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Neonates and patients with liver dysfunction start lower
Bivalirudin: 0.125 to 0.2 mg/kg/h; adjust for renal function
Fondaparinux: limited pediatric data; specialist guidance required
Rivaroxaban: weight-based dosing in children >12 years with data emerging
Duration and follow-up
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Same principles as adults for anticoagulation duration
Platelet recovery monitored every 1 to 2 days
Hematology involvement essential for all pediatric HIT
Background
Epidemiology
Incidence and prevalence
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HIT occurs in 0.2% to 5% of heparin-exposed patients overall
UFH risk: surgical patients 1% to 5%, medical patients 0.1% to 1%
LMWH risk: approximately 10-fold lower than UFH
Cardiac surgery patients among highest risk: 1% to 5%
Orthopedic surgery comparable to cardiac surgery in HIT risk
Demographics
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Female sex approximately twice the risk of male patients
All ages affected; rare in children but increasingly recognized
Prior heparin exposure within 100 days increases rapid-onset HIT risk
Outcomes data
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Untreated HIT: thrombosis rate approximately 5% per day
Thromboembolic complications develop in approximately 50% of untreated confirmed cases
Contemporary multicenter cohort (n=119 confirmed HIT): VTE 23%, arterial thromboembolism 9%, major bleeding 12.6%, mortality 18%
DIC complicates up to 20% of HIT cases
Skin necrosis occurs in 10% to 20% of HIT cases
Pathophysiology
Immune mechanism
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IgG antibodies form against PF4/heparin complexes on platelet surface
PF4 is a platelet alpha-granule protein released on platelet activation
Heparin binds PF4 and alters its conformation creating a neoantigen
IgG antibodies recognize PF4/heparin complex and bind FcgammaRIIA on platelet surface
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Platelet activation and aggregation
Prothrombotic microparticle release
Platelet consumption causing thrombocytopenia
Simultaneous monocyte and endothelial cell activation
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Tissue factor upregulation
Thrombin generation
Massive thrombotic tendency
Paradox of thrombosis not bleeding
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Despite thrombocytopenia, platelet activation creates a hypercoagulable state
Thrombin generation far exceeds hemostatic threshold
Venous > arterial thrombosis 4:1 ratio
Arterial thrombosis from platelet-rich white clots and embolism
Antibody kinetics
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IgG HIT antibodies typically detectable within 5 to 14 days of first heparin exposure
Antibodies become undetectable within approximately 100 days
Re-exposure within 100 days of prior exposure triggers rapid-onset HIT
Autoimmune HIT: antibodies can activate platelets without heparin present
Therapeutic Considerations
Why heparin must stop completely
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Any residual heparin continues antibody-mediated platelet activation
LMWH cross-reacts with HIT antibodies in approximately 90% of cases
Flushing with saline instead of heparin critical
Even heparin-coated catheters contribute to antigen load
Anticoagulation despite thrombocytopenia
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Counterintuitive but essential — thrombotic risk dominates bleeding risk in HIT
Therapeutic anticoagulation required even for isolated HIT without thrombosis
Platelet transfusion avoided — feeds the thrombotic cycle
Warfarin timing restriction
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Warfarin depletes protein C before factors II, VII, IX, X
Early warfarin in active HIT worsens protein C depletion
Results in a transient hypercoagulable state and venous limb gangrene risk
Must have adequate non-heparin anticoagulation and platelet recovery before warfarin
Evolving evidence
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DOACs increasingly used for HIT management — rivaroxaban most data
ASH 2018 guidelines provide conditional recommendations for DOAC use
Monoclonal antibody pathogenesis research ongoing (NEJM 2025)
NCCN guidelines relevant for cancer-associated HIT and VITT management
Patient Discharge Instructions
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HIT diagnosis home care
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Blood thinner medication taken exactly as prescribed every day
Do not stop anticoagulation without speaking to your doctor
Duration of blood thinners: at least 4 weeks if no clot; at least 3 months if a blood clot was found
Avoid all heparin products — inform every doctor, nurse, pharmacist, and dentist of your HIT diagnosis before any procedure
Medical alert bracelet or wallet card documenting HIT strongly recommended
Warning signs to return to emergency room immediately
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Sudden leg swelling, pain, or redness in one leg
Chest pain or shortness of breath
Sudden weakness, numbness, vision change, or difficulty speaking
Severe abdominal pain
Cold, pale, painful, or discolored hand or foot
Signs of bleeding: blood in urine or stool, unusual bruising, prolonged bleeding from cuts
Skin turning black or dying at any injection site
Follow-up instructions
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Blood specialist (hematologist) appointment within 1 to 2 weeks
Platelet count recheck as directed — usually every 1 to 2 days until normal
INR or other blood thinner monitoring as prescribed
Future heparin avoidance
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HIT antibodies disappear after about 100 days — this does NOT mean heparin is safe to use again without specialist evaluation
Future cardiac or vascular surgery requiring heparin needs specialist planning
Inform all future emergency departments and hospitals of HIT diagnosis
References
Guidelines and key sources
Society guidelines
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American Society of Hematology 2018 Guidelines for Management of VTE: Heparin-Induced Thrombocytopenia
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Cuker A, Arepally GM, Chong BH, et al. Blood Advances. 2018
PMCID PMC6258919
ACCP Antithrombotic Therapy and Prevention of Thrombosis 9th Edition
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Linkins LA, Dans AL, Moores LK, et al. Chest. 2012
PMCID PMC3278058
NCCN Cancer-Associated Venous Thromboembolic Disease Guidelines 2026
Landmark studies and reviews
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Greinacher A. Heparin-Induced Thrombocytopenia. NEJM. 2015
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Comprehensive mechanism, diagnosis, and treatment review
Cuker A, Gimotty PA, Crowther MA, Warkentin TE. Predictive Value of the 4Ts Scoring System: Systematic Review and Meta-Analysis. Blood. 2012
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Validated 4Ts NPV 97% to 99% for low-probability score
Salter BS, Weiner MM, Trinh MA, et al. Heparin-Induced Thrombocytopenia: A Comprehensive Clinical Review. JACC. 2016
Warkentin TE. Clinical Picture of HIT and Its Differentiation From Non-HIT Thrombocytopenia. Thrombosis and Haemostasis. 2016
Nilius H, Sinitsa E, Studt JD, et al. Outcomes of Patients With Suspected HIT in a Contemporary Multicenter Cohort. Blood Advances. 2025
Larsen EL, Nilius H, Studt JD, et al. Accuracy of Diagnosing HIT. JAMA Network Open. 2024
Treverton J, Arnold DM, Ivanov DG, et al. Monoclonal Antibodies in the Pathogenesis of HIT. NEJM. 2025
Coding and classification
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ICD-10 D75.82 heparin-induced thrombocytopenia
ICD-10 T45.515A adverse effect of anticoagulants
SNOMED CT heparin-induced thrombocytopenia disorder
SymptomDx is an educational tool for medical professionals. It does not replace clinical judgment. Verify all clinical data and drug dosages with authoritative sources.
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Management Protocols
Heparin-Induced Thrombocytopenia (HIT)