26.1 Hematologic Emergencies in the ICU: HIT, DIC, TMA & Anticoagulant Reversal

ABIM Critical Care Medicine Study Guide Exam

Track your progress as you read

Finished sections get a check mark.

1 Chapter 1: Exam Orientation: Format, Blueprint & Study Strategy

1.1 ABIM Critical Care Medicine Exam: Format, Blueprint & Study Strategy

2 Chapter 2: Acute Respiratory Failure & ARDS

2.1 ARDS Definition, Pathophysiology & Phenotypes 2.2 Lung-Protective Mechanical Ventilation 2.3 Refractory ARDS: Prone Positioning, Neuromuscular Blockade & VV-ECMO

3 Chapter 3: Obstructive Airways, Pulmonary Vascular & Pleural Emergencies

3.1 Severe Asthma & COPD Exacerbations in the ICU 3.2 Massive & Submassive Pulmonary Embolism 3.3 Pulmonary Hypertension & Right Ventricular Failure in the ICU 3.4 Massive Hemoptysis, Complex Pleural Effusions & Thoracic Drainage

4 Chapter 4: Airway, Parenchymal & Nonthrombotic Pulmonary Emergencies

4.1 Airway Management, Upper-Airway Obstruction & Artificial-Airway Complications 4.2 Diffuse Alveolar Hemorrhage, Interstitial Lung Disease, Pulmonary Vasculitis & Noncardiogenic Edema 4.3 Severe Community-Acquired & Viral Pneumonia 4.4 Nonthrombotic Embolism (Air, Fat, Amniotic Fluid, Tumor, Septic) & Acute Chest Syndrome

5 Chapter 5: Mechanical Ventilation Modes, Dyssynchrony & Liberation

5.1 Mechanical Ventilator Modes & Advanced Breath Delivery 5.2 Patient-Ventilator Dyssynchrony & Waveform Analysis 5.3 Ventilator Liberation, Spontaneous Breathing Trials & Post-Extubation Support

6 Chapter 6: Shock Syndromes & Hemodynamic Principles

6.1 Shock Classification, Cellular Pathophysiology & Biomarkers 6.2 Hemodynamic Monitoring: Arterial Lines, CVP & Pulmonary Artery Catheter 6.3 Dynamic Assessment of Fluid Responsiveness & Resuscitation Targets

7 Chapter 7: Vasoactive Therapies & Mechanical Circulatory Support

7.1 Vasopressors & Inotropes: Pharmacology & Clinical Titration 7.2 Temporary Mechanical Circulatory Support: IABP, Impella & TandemHeart 7.3 Venoarterial ECMO (VA-ECMO) & Differential Hypoxemia 7.4 Post-Cardiac Arrest Care, Targeted Temperature Management & Neuroprognostication

8 Chapter 8: Acute Kidney Injury & Renal Replacement Therapy

8.1 KDIGO AKI Classification, Etiologies & Diagnostic Evaluation 8.2 Continuous Renal Replacement Therapy (CRRT) vs Intermittent Hemodialysis 8.3 Indications & Timing for RRT in Critical Illness: AKIKI & STARRT-AKI

9 Chapter 9: Electrolyte, Acid-Base & Endocrine Emergencies

9.1 Severe Dysnatremias: Hyponatremia, Hypernatremia & Osmotic Demyelination 9.2 Potassium, Calcium, Magnesium & Phosphate Disorders 9.3 Complex & Mixed Acid-Base Disorders: Boston vs Copenhagen vs Stewart 9.4 Endocrine Crises: DKA, HHS, Thyroid Storm, Myxedema Coma & Adrenal Crisis

10 Chapter 10: Glycemic Control, Hyperammonemia, Pituitary & Adrenal Disorders

10.1 ICU Glycemic Control & Severe Hypoglycemia 10.2 Non-Hepatic Hyperammonemia & Metabolic Encephalopathy 10.3 Pituitary Emergencies, Adrenal Excess & Critical Illness-Related Corticosteroid Insufficiency

11 Chapter 11: Acute Coronary Syndromes & Cardiac Arrhythmias

11.1 Acute Coronary Syndromes & Mechanical Complications of Myocardial Infarction 11.2 Critical Tachyarrhythmias: Atrial Fibrillation with RVR, VT & VF 11.3 Critical Bradyarrhythmias, Conduction Blocks & Temporary Cardiac Pacing

12 Chapter 12: Acute Heart Failure, Valvular & Pericardial Emergencies

12.1 Acute Decompensated Heart Failure & Cardiogenic Pulmonary Edema 12.2 Acute Valvular Regurgitation & Prosthetic Valve Emergencies 12.3 Pericardial Tamponade & Acute Aortic Syndromes

13 Chapter 13: Myocardial Disease, Hypertensive & Cardiac Device Emergencies

13.1 Fulminant Myocarditis, Stress & Peripartum Cardiomyopathy, and Hypertrophic Cardiomyopathy 13.2 Hypertensive Emergencies & Ruptured Abdominal Aortic Aneurysm 13.3 Implanted Cardiac Devices, LVAD Emergencies & Electrical Storm

14 Chapter 14: Sepsis & Systemic Infectious Diseases

14.1 Sepsis-3 Definitions & Surviving Sepsis Campaign 2026 Guidelines 14.2 Refractory Septic Shock & Adjunctive Therapies 14.3 Multidrug-Resistant Pathogens & Antimicrobial Stewardship in the ICU

15 Chapter 15: ICU-Acquired & Severe Focal Infections

15.1 Hospital-Acquired & Ventilator-Associated Pneumonia 15.2 Central Line-Associated Bloodstream Infections & Catheter-Associated UTIs 15.3 Intra-Abdominal Sepsis, Necrotizing Soft Tissue Infections & CNS Infections

16 Chapter 16: Focal, Special-Host & Systemic Infections

16.1 CNS Infections Beyond Bacterial Meningitis: Encephalitis, Brain Abscess & Epidural Abscess 16.2 Infections in the Immunocompromised Host, Tropical & Bioterror Infections 16.3 Infective Endocarditis, Device Infections & Other Focal Cardiovascular Infections 16.4 Antimicrobial Pharmacokinetics, Allergy, Toxicity & Infection Prevention 16.5 Gastrointestinal & Hepatobiliary Infections: Fulminant C. difficile, Typhlitis, CMV Colitis & Abscesses

17 Chapter 17: Neurocritical Care & Coma

17.1 Coma, Altered Mental Status & Acute Delirium in the ICU 17.2 Status Epilepticus & Non-Convulsive Status Epilepticus 17.3 Acute Ischemic Stroke & Intracranial Hemorrhage

18 Chapter 18: Cerebrovascular Syndromes, Encephalopathy & Withdrawal States

18.1 Cerebral Venous Sinus Thrombosis, PRES & Reversible Cerebral Vasoconstriction Syndrome 18.2 Alcohol & Sedative Withdrawal, Wernicke Encephalopathy & Drug-Induced Encephalopathy

19 Chapter 19: Intracranial Hypertension & Neuromuscular Weakness

19.1 Intracranial Pressure Monitoring, Cerebral Perfusion & Tiered ICP Management 19.2 Acute Neuromuscular Respiratory Failure, ICU-Acquired Weakness & Brain Death Determination

20 Chapter 20: Traumatic Brain Injury, Spinal Cord Injury & Toxin-Mediated Paralysis

20.1 Traumatic Brain Injury Management & Paroxysmal Sympathetic Hyperactivity 20.2 Acute Spinal Cord Injury, Neurogenic Shock & Autonomic Dysreflexia 20.3 Toxin-Mediated Paralysis & Neuromuscular Crises: Botulism, Tetanus, Tick Paralysis & Myasthenic Crisis

21 Chapter 21: Gastrointestinal, Hepatic & Abdominal Emergencies

21.1 Acute Upper & Lower Gastrointestinal Bleeding in the ICU 21.2 Acute Liver Failure & Severe Acute Pancreatitis 21.3 Abdominal Compartment Syndrome & Acute Mesenteric Ischemia

22 Chapter 22: Luminal GI Emergencies & Complications of Cirrhosis

22.1 Esophageal, Gastric & Bowel Emergencies: Perforation, Obstruction, Ogilvie Syndrome & Colonic Ischemia 22.2 Complications of Cirrhosis: Alcohol-Associated Hepatitis, Hepatorenal Syndrome & Pulmonary Vascular Syndromes

23 Chapter 23: Trauma, Burns & Perioperative Critical Care

23.1 Polytrauma Resuscitation, Damage Control & Massive Transfusion 23.2 Severe Burn Injury, Inhalation Injury & Environmental Emergencies 23.3 Perioperative Critical Care for High-Risk Surgical Patients

24 Chapter 24: Thoracic Trauma, Environmental Injury & Obstetric Critical Care

24.1 Thoracic Trauma: Flail Chest, Pulmonary Contusion, Great Vessel & Tracheobronchial Injury 24.2 Environmental Injury: Drowning, Diving, Altitude, Heat, Cold, Electrical & Radiation 24.3 Obstetric & Genitourinary Emergencies and the Physiology of Pregnancy

25 Chapter 25: Transplantation, Donor Management & Post-Cardiac Surgery Care

25.1 Solid Organ Transplant Recipients & Deceased Donor Management 25.2 Post-Cardiac Surgery Critical Care: Bleeding, Tamponade, Low Output & Vasoplegia

26 Chapter 26: Hematologic Emergencies, Toxicology, Critical Ultrasound & ICU Liberation

26.1 Hematologic Emergencies in the ICU: HIT, DIC, TMA & Anticoagulant Reversal 26.2 Critical Care Toxicology, Toxidromes & Specific Antidotes 26.3 Critical Care Point-of-Care Ultrasound (POCUS) 26.4 ICU Liberation, Analgosedation, Goals of Care & Critical Care Ethics

27 Chapter 27: Transfusion Medicine, Hematologic & Oncologic Disorders

27.1 Transfusion Medicine: Products, Thresholds, Reactions & Apheresis 27.2 Red and White Cell Disorders, Hemoglobinopathies, Factor Deficiencies & Hypercoagulable States 27.3 Oncologic Emergencies, Hematopoietic Cell Transplant Complications & Cellular Therapy Toxicity

28 Chapter 28: Clinical Pharmacology, Adverse Drug Reactions & Specific Poisonings

28.1 Pharmacokinetic Principles, Dose Adjustment & Drug Interactions in Critical Illness 28.2 Adverse Drug Reactions: Anaphylaxis, Severe Cutaneous Reactions & Hyperthermic Syndromes 28.3 Specific Poisonings: Sodium-Channel Blockers, Lithium, Valproate, Theophylline, Iron, Sulfonylureas & Methemoglobinemia

29 Chapter 29: Ethics, Research Methods, Administration & Abdominal Ultrasound

29.1 Advance Care Planning, Nonbeneficial Treatment, Informed Consent & Confidentiality 29.2 Critical Care Research Methods, Statistics, IRB Oversight & Quality Improvement 29.3 Abdominal, Vascular & Procedural Point-of-Care Ultrasound

26.1 Hematologic Emergencies in the ICU: HIT, DIC, TMA & Anticoagulant Reversal

Key Takeaways Explain This Topic AI

A 4T score of 6 to 8 indicates high probability of Heparin-Induced Thrombocytopenia (HIT); management mandates immediate cessation of all heparin exposures and initiation of a non-heparin direct thrombin inhibitor (argatroban or bivalirudin) without awaiting confirmatory Serotonin Release Assay (SRA) results.

Warfarin is strictly contraindicated during acute HIT and must never be administered until platelet counts fully recover (>= 150 x 10^9/L) due to rapid protein C depletion precipitating microvascular thrombosis and catastrophic venous limb gangrene.

Disseminated Intravascular Coagulation (DIC) requires aggressive control of the inciting trigger alongside targeted transfusion support; maintain fibrinogen > 150 mg/dL (or > 200 mg/dL in severe obstetric hemorrhage) using cryoprecipitate, while avoiding antifibrinolytic agents in prothrombotic or septic phenotypes.

Thrombotic Thrombocytopenic Purpura (TTP) is a medical emergency driven by severe ADAMTS13 deficiency (< 10%) that requires immediate therapeutic plasma exchange (TPE), high-dose corticosteroids, and caplacizumab; platelet transfusions are contraindicated because they precipitate acute microvascular thrombosis.

Life-threatening anticoagulant-associated hemorrhage requires immediate factor-specific reversal: 4-factor prothrombin complex concentrate (4F-PCC) plus intravenous vitamin K for warfarin; idarucizumab for dabigatran; 4F-PCC for factor Xa inhibitors (andexanet alfa was withdrawn from the US market in December 2025); and protamine sulfate for unfractionated heparin.

Last updated: October 2026

Heparin-Induced Thrombocytopenia (HIT)

Heparin-Induced Thrombocytopenia (Type II HIT) is a life-threatening, immune-mediated prothrombotic adverse drug reaction. Unlike the benign, non-immune Type I heparin-associated thrombocytopenia—a mild, transient drop occurring within the first 48 to 72 hours due to direct platelet agglutination—Type II HIT is driven by immunoglobulin G (IgG) autoantibodies directed against multimolecular complexes of platelet factor 4 (PF4) and unfractionated heparin (UFH) or, less frequently, low-molecular-weight heparin (LMWH).

Pathophysiology and Thrombus Generation

When heparin binds to PF4 released from platelet alpha granules, conformational changes expose neoepitopes on PF4. Pathogenic IgG antibodies bind these PF4-heparin complexes, and their Fc domains subsequently cross-link platelet Fc γ \gamma γ RIIa receptors. This cross-linking triggers intense platelet activation, releasing procoagulant microparticles, additional PF4, and excessive thrombin. Concurrently, PF4 binds to heparan sulfate on endothelial surfaces, enabling antibody binding and subsequent endothelial injury and tissue factor expression. The net result is a consumptive thrombocytopenia accompanied by a paradoxically profound hypercoagulable state ("white clot syndrome"), causing both venous thromboembolism (deep vein thrombosis, pulmonary embolism, cerebral venous sinus thrombosis) and arterial thrombosis (limb ischemia, stroke, acute myocardial infarction, mesenteric ischemia).

Clinical Risk Stratification: The 4T Scoring System

The pretest probability of HIT should be systematically calculated using the validated 4T Score :

Thrombocytopenia :

2 points : Platelet count fall > 50 % > 50\% > 50% and platelet nadir ≥ 20 × 10 9 / L \ge 20 \times 10^9/\text{L} ≥ 20 × 1 0 9 / L .

1 point : Platelet count fall 30 % 30\% 30% to 50 % 50\% 50% or platelet nadir 10 10 10 to 19 × 10 9 / L 19 \times 10^9/\text{L} 19 × 1 0 9 / L .

0 points : Platelet count fall < 30 % < 30\% < 30% or platelet nadir < 10 × 10 9 / L < 10 \times 10^9/\text{L} < 10 × 1 0 9 / L .

Timing of Platelet Count Fall :

2 points : Clear onset between days 5 and 10 of heparin exposure, or ≤ 1 \le 1 ≤ 1 day if heparin exposure occurred within the past 30 days.

1 point : Consistent with day 5 to 10 fall, but missing platelet counts, or onset after day 10, or ≤ 1 \le 1 ≤ 1 day with heparin exposure within the past 30 to 100 days.

0 points : Platelet fall occurs < 4 < 4 < 4 days without recent heparin exposure.

Thrombosis or Other Sequelae :

2 points : Confirmed new thrombosis, skin necrosis at heparin injection sites, or acute systemic reaction after intravenous heparin bolus (chills, tachycardia, hypertension, dyspnea).

1 point : Progressive or recurrent thrombosis, erythematous skin lesions, or suspected (unproven) thrombosis.

0 points : None.

oTher Causes of Thrombocytopenia :

2 points : No alternative cause evident.

1 point : Possible alternative etiology identified (e.g., severe sepsis, post-cardiac surgery day 1 to 3, balloon pump).

0 points : Definite alternative cause present.

Total 4T Score Pretest Probability Estimated Risk of HIT Clinical Action

0 to 3 points Low Probability < 1 % − 2 % < 1\% - 2\% < 1% − 2% Heparin can be safely continued; evaluate alternative causes of thrombocytopenia. Routine antibody testing is not indicated.

4 to 5 points Intermediate Probability ∼ 10 % − 14 % \sim 10\% - 14\% ∼ 10% − 14% Discontinue all heparin immediately. Order PF4-heparin immunoassay. Initiate non-heparin therapeutic anticoagulation.

6 to 8 points High Probability ∼ 64 % − 80 % \sim 64\% - 80\% ∼ 64% − 80% Discontinue all heparin immediately. Order PF4-heparin immunoassay and functional assay. Initiate non-heparin direct thrombin inhibitor immediately.

Diagnostic Laboratory Testing

PF4-Heparin Polyspecific or IgG-Specific ELISA : Highly sensitive ( > 99 % > 99\% > 99% ) with a high negative predictive value. A negative ELISA virtually excludes HIT. However, false positives are frequent, particularly in cardiac surgery cohorts where non-activating antibodies arise. An optical density (OD) > 0.40 > 0.40 > 0.40 is considered positive, but higher values correlate directly with pathogenic potential (OD > 2.0 > 2.0 > 2.0 has a positive predictive value > 90 % > 90\% > 90% ).

Serotonin Release Assay (SRA) : The definitive gold-standard functional assay. Washed donor platelets are incubated with patient serum and varying concentrations of heparin. A positive SRA demonstrates > 20 % > 20\% > 20% 14 C ^{14}\text{C} 14 C -serotonin release at therapeutic heparin levels ( 0.1 − 0.3 U/mL 0.1 - 0.3\text{ U/mL} 0.1 − 0.3 U/mL ) and inhibition of release at supratherapeutic heparin levels ( 100 U/mL 100\text{ U/mL} 100 U/mL ). Clinicians must never delay treatment while awaiting SRA results.

Acute Management and Pharmacotherapy

Immediate Cessation of Heparin : Stop all UFH infusions, LMWH injections, heparin flushes, heparin-coated invasive vascular catheters (e.g., pulmonary artery catheters), and continuous renal replacement circuit flushes.

Immediate Initiation of Non-Heparin Anticoagulation : Even in the absence of documented thrombosis, therapeutic-dose non-heparin anticoagulation is mandatory because the risk of subsequent thrombosis exceeds 50 % 50\% 50% over the ensuing 30 days:

Argatroban : Synthetic univalent direct thrombin inhibitor (DTI). Metabolized exclusively by the liver; preferred in patients with acute kidney injury or renal replacement therapy. Standard initial dose is 2 mcg/kg/min 2\text{ mcg/kg/min} 2 mcg/kg/min IV continuous infusion (reduced to 0.5 mcg/kg/min 0.5\text{ mcg/kg/min} 0.5 mcg/kg/min in moderate/severe hepatic impairment, heart failure, critical illness, or post-cardiac surgery). Monitored using activated partial thromboplastin time (aPTT), with a target of 1.5 1.5 1.5 to 3.0 3.0 3.0 times baseline (typically 45 to 90 seconds). Argatroban cross-reacts with prothrombin time reagents, significantly elevating the INR.

Bivalirudin : Bivalent reversible direct thrombin inhibitor. Cleared predominantly via enzymatic proteolysis ( 80 % 80\% 80% ) with minor renal elimination ( 20 % 20\% 20% ). Preferred in patients with hepatic dysfunction or in those requiring acute percutaneous coronary intervention or cardiopulmonary bypass. Initial dose is 0.15 − 0.2 mg/kg/h 0.15 - 0.2\text{ mg/kg/h} 0.15 − 0.2 mg/kg/h , titrated to an aPTT of 1.5 1.5 1.5 to 2.5 2.5 2.5 times baseline.

Fondaparinux & DOACs : Off-label alternatives used in hemodynamically stable, non-critically ill patients without renal compromise.

Warning

Strict Warfarin Contraindication in Acute HIT : Warfarin must never be administered during the acute phase of HIT, nor should it be used as a monotherapy before platelet count recovery. Warfarin rapidly depletes protein C (half-life ∼ 6 hours \sim 6\text{ hours} ∼ 6 hours ) before factor X and prothrombin are cleared, creating a transient, severe hypercoagulable state. In the setting of uncontrolled thrombin generation, this precipitates widespread microvascular thrombosis, extensive cutaneous necrosis, and catastrophic venous limb gangrene (phlegmasia cerulea dolens). If a patient is already taking warfarin when HIT is diagnosed, immediately reverse it with intravenous vitamin K ( 10 mg 10\text{ mg} 10 mg ). Warfarin can only be safely reintroduced once the platelet count has completely normalized ( ≥ 150 × 10 9 / L \ge 150 \times 10^9/\text{L} ≥ 150 × 1 0 9 / L ), overlapped with a non-heparin DTI for a minimum of 5 days, and continued until the INR is therapeutic for two consecutive days.

Note

Platelet Transfusion Restriction : Prophylactic platelet transfusions are contraindicated in HIT because infused platelets bind circulating PF4-heparin complexes, fueling microvascular thrombosis. Platelet transfusions should be reserved exclusively for overt, life-threatening hemorrhage.

Disseminated Intravascular Coagulation (DIC)

Disseminated Intravascular Coagulation is a secondary clinicopathologic syndrome marked by systemic, uncontrolled intravascular activation of coagulation, leading to microvascular fibrin deposition, tissue ischemia, multi-organ dysfunction, and eventual exhaustion of platelets and clotting factors, culminating in severe hemorrhagic diathesis.

Etiologies and Pathophysiology

Common triggers include severe sepsis (endotoxin and cytokine-mediated tissue factor expression), major trauma, crush injury, acute pancreatitis, obstetrical catastrophes (amniotic fluid embolism, abruptio placentae), severe burns, acute promyelocytic leukemia, and metastatic adenocarcinomas. The central driver is unregulated thrombin generation resulting from excessive tissue factor-factor VIIa pathway activation, accompanied by severe downregulation of endogenous anticoagulant pathways (antithrombin III, protein C, tissue factor pathway inhibitor) and impaired fibrinolysis due to sustained plasminogen activator inhibitor-1 (PAI-1) release.

Diagnostic Scoring (ISTH Overt DIC Criteria)

The International Society on Thrombosis and Haemostasis (ISTH) overt DIC score utilizes four readily accessible laboratory parameters in patients with an identifiable underlying disorder:

Platelet count : > 100 × 10 9 / L > 100 \times 10^9/\text{L} > 100 × 1 0 9 / L (0 pts); 50 50 50 to 100 × 10 9 / L 100 \times 10^9/\text{L} 100 × 1 0 9 / L (1 pt); < 50 × 10 9 / L < 50 \times 10^9/\text{L} < 50 × 1 0 9 / L (2 pts).

Fibrin-related markers (D-dimer / FDP) : No increase (0 pts); moderate increase (2 pts); strong increase (3 pts).

Prolonged prothrombin time (PT) : < 3 s < 3\text{ s} < 3 s prolongation (0 pts); 3 3 3 to 6 s 6\text{ s} 6 s prolongation (1 pt); > 6 s > 6\text{ s} > 6 s prolongation (2 pts).

Fibrinogen level : > 100 mg/dL > 100\text{ mg/dL} > 100 mg/dL (0 pts); < 100 mg/dL < 100\text{ mg/dL} < 100 mg/dL (1 pt).

A cumulative score ≥ 5 \ge 5 ≥ 5 points is diagnostic of overt DIC and correlates with high intensive care unit mortality.

Targeted ICU Transfusion Protocols in DIC

Definitive therapy requires immediate eradication of the underlying etiology (source control, antimicrobial therapy, delivery of the placenta, surgical repair). Routine transfusion to correct abnormal laboratory values in non-bleeding patients is not recommended. When active bleeding or an invasive procedural requirement occurs, supportive therapy follows explicit targets:

Fibrinogen Replacement Target : Fibrinogen is an acute-phase reactant; a normal or borderline low level in severe sepsis or trauma indicates rapid consumption. Maintain fibrinogen > 150 mg/dL > 150\text{ mg/dL} > 150 mg/dL (or > 200 mg/dL > 200\text{ mg/dL} > 200 mg/dL in severe obstetric hemorrhage or trauma). Cryoprecipitate is the intervention of choice: 1 adult pool (10 units) provides approximately 2 2 2 to 3 g 3\text{ g} 3 g of fibrinogen along with factor VIII, von Willebrand factor, and factor XIII, typically increasing plasma fibrinogen by 50 50 50 to 100 mg/dL 100\text{ mg/dL} 100 mg/dL . Fibrinogen concentrate ( 30 − 60 mg/kg 30 - 60\text{ mg/kg} 30 − 60 mg/kg ) is an equivalent alternative when volume overload is a concern.

Platelet Transfusion Target : Transfuse to maintain platelets ≥ 50 × 10 9 / L \ge 50 \times 10^9/\text{L} ≥ 50 × 1 0 9 / L in actively bleeding patients or those requiring major invasive interventions. In non-bleeding patients, prophylactic transfusion is reserved for counts < 10 < 10 < 10 to 20 × 10 9 / L 20 \times 10^9/\text{L} 20 × 1 0 9 / L .

Coagulation Factor Replacement : Administer Fresh Frozen Plasma (FFP, 15 − 25 mL/kg 15 - 25\text{ mL/kg} 15 − 25 mL/kg ) in actively bleeding patients with significant PT/INR ( > 1.5 − 2.0 > 1.5 - 2.0 > 1.5 − 2.0 ) or aPTT prolongation. Prothrombin complex concentrates (4F-PCC) are generally avoided in DIC due to thrombogenic risks from procoagulant factor accumulation in the absence of balanced anticoagulant replenishment.

Antifibrinolytic Contraindication : Tranexamic acid (TXA) and aminocaproic acid are contraindicated in classic sepsis-induced or prothrombotic DIC because blocking fibrinolysis while systemic microvascular thrombosis is active causes fatal organ ischemia, such as bilateral renal cortical necrosis. Antifibrinolytics are reserved solely for hyperfibrinolytic DIC phenotypes (e.g., acute promyelocytic leukemia or documented severe hyperfibrinolysis on thromboelastography).

Thrombotic Microangiopathies: TTP vs. HUS

Thrombotic Microangiopathies (TMAs) are characterized by the clinical triad of microangiopathic hemolytic anemia (MAHA), consumptive thrombocytopenia, and microvascular thrombosis causing ischemic organ injury.

Thrombotic Thrombocytopenic Purpura (TTP)

TTP is caused by a severe deficiency of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity to < 10 % < 10\% < 10% . Under physiological conditions, ADAMTS13 cleaves ultra-large von Willebrand factor (UL-vWF) multimers secreted by endothelial cells. In the absence of functional ADAMTS13—most commonly due to acquired IgG autoantibodies—UL-vWF multimers accumulate, tethering circulating platelets under high vascular shear stress. This produces disseminated platelet-rich microthrombi in arterioles and capillaries without significant activation of the soluble coagulation cascade (coagulation times, PT/INR, aPTT, and fibrinogen remain typically normal).

Clinical Presentation and Diagnostic Stratification

The historic pentad of TTP (thrombocytopenia, MAHA, fluctuating neurologic symptoms, fever, renal dysfunction) is present in < 10 % < 10\% < 10% of patients. Modern diagnosis requires only the dyad of unexplained microangiopathic hemolytic anemia (schistocytes on peripheral blood smear, high LDH, low/undetectable haptoglobin, negative direct antiglobulin test) and profound thrombocytopenia.

The PLASMIC Score predicts severe ADAMTS13 deficiency ( < 10 % < 10\% < 10% ):

Platelet count < 30 × 10 9 / L < 30 \times 10^9/\text{L} < 30 × 1 0 9 / L (1 pt)

Combined hemolysis markers (reticulocyte count > 2.5 % > 2.5\% > 2.5% , undetectable haptoglobin, or indirect bilirubin > 2.0 mg/dL > 2.0\text{ mg/dL} > 2.0 mg/dL ) (1 pt)

• No active cancer within past year (1 pt)
• No history of solid organ or stem cell transplant (1 pt)
• MCV < 90 fL < 90\text{ fL} < 90 fL (1 pt)
• INR < 1.5 < 1.5 < 1.5 (1 pt)
• Serum creatinine < 2.0 mg/dL < 2.0\text{ mg/dL} < 2.0 mg/dL (1 pt)

A PLASMIC score of 6 to 7 indicates high probability ( 62 % − 82 % 62\% - 82\% 62% − 82% ) of severe ADAMTS13 deficiency and mandates immediate empiric intervention prior to receiving definitive ADAMTS13 laboratory results.

Emergent TTP Management Protocol

Therapeutic Plasma Exchange (TPE) : Emergent daily 1.0 1.0 1.0 to 1.5 1.5 1.5 plasma volume exchanges with FFP or cryosupernatant plasma. TPE removes anti-ADAMTS13 autoantibodies and circulating UL-vWF multimers while replenishing active ADAMTS13 enzyme. Initiating TPE within hours of presentation reduces mortality from > 90 % > 90\% > 90% to < 15 % < 15\% < 15% .

Systemic Immunosuppression : High-dose intravenous methylprednisolone ( 1 g/day 1\text{ g/day} 1 g/day for 3 days or 1 mg/kg/day 1\text{ mg/kg/day} 1 mg/kg/day ) to suppress anti-ADAMTS13 antibody synthesis, coupled with early administration of Rituximab ( 375 mg/m 2 375\text{ mg/m}^2 375 mg/m 2 weekly for 4 doses).

Caplacizumab : A bivalent humanized nanobody that targets the A1 domain of vWF, inhibiting the interaction between UL-vWF and the platelet glycoprotein Ib-IX-V receptor. Administered as an initial 10 mg 10\text{ mg} 10 mg IV bolus prior to plasma exchange, followed by daily 11 mg 11\text{ mg} 11 mg subcutaneous injections (US labeling; 10 mg 10\text{ mg} 10 mg in Europe) post-TPE and continued for 30 days following cessation of TPE. Caplacizumab rapidly arrests platelet aggregation, shortens time to platelet count normalization, and dramatically lowers TTP exacerbations and refractoriness.

Absolute Avoidance of Platelet Transfusions : Platelet transfusions in TTP are strictly contraindicated because they provide substrate for accelerated microvascular thrombosis, precipitating acute myocardial infarction, stroke, and sudden cardiac death. Platelets are administered only in the presence of immediate life-threatening hemorrhage (e.g., catastrophic intracranial hemorrhage).

Note

Distinguishing TTP from HUS : Hemolytic Uremic Syndrome (STEC-HUS) is caused by Shiga toxin-producing Escherichia coli (O157:H7) causing endothelial apoptosis, presenting with a diarrheal prodrome and predominant acute anuric renal failure with normal ADAMTS13 activity. Atypical HUS (aHUS) is mediated by uncontrolled activation of the alternative complement pathway (mutations in complement Factor H, I, B, or membrane cofactor protein) and is treated with terminal complement C5 inhibitors ( eculizumab or ravulizumab ).

Anticoagulant Reversal in Life-Threatening Hemorrhage

Immediate reversal of systemic anticoagulation is essential in patients presenting with intracranial hemorrhage, massive gastrointestinal bleeding, or requiring emergency surgical interventions.

Anticoagulant Drug Class Specific Reversal Agent(s) Mechanism of Action Clinical Dosing & Administration Protocol

Warfarin (Vitamin K Antagonist) 4-Factor Prothrombin Complex Concentrate (4F-PCC) plus Intravenous Vitamin K Replenishes inactive factors II, VII, IX, X and proteins C and S; vitamin K restores hepatic synthesis 4F-PCC dosed by pre-treatment INR: INR 2.0-3.9 ( 25 U/kg 25\text{ U/kg} 25 U/kg , max 2500 U); INR 4.0-6.0 ( 35 U/kg 35\text{ U/kg} 35 U/kg , max 3500 U); INR > 6.0 >6.0 > 6.0 ( 50 U/kg 50\text{ U/kg} 50 U/kg , max 5000 U) or fixed dose 1500-2000 U IV. Administer concurrent Vitamin K 10 mg 10\text{ mg} 10 mg slow IV in 50 mL 50\text{ mL} 50 mL saline over 30 min 30\text{ min} 30 min to prevent rebound coagulopathy.

Dabigatran (Direct Thrombin Inhibitor) Idarucizumab Humanized Fab fragment binding free and thrombin-bound dabigatran with 350x higher affinity than thrombin 5 g 5\text{ g} 5 g IV total , administered as two consecutive 2.5 g 2.5\text{ g} 2.5 g boluses/infusions. Immediate complete reversal. If unavailable, hemodialysis removes ∼ 60 % − 70 % \sim 60\% - 70\% ∼ 60% − 70% of dabigatran.

Oral Factor Xa Inhibitors (Apixaban, Rivaroxaban, Edoxaban) 4F-PCC ( 50 units/kg 50\text{ units/kg} 50 units/kg ); andexanet alfa was withdrawn from the US market effective December 22, 2025 Andexanet was a recombinant modified decoy factor Xa protein lacking catalytic activity that sequestered FXa inhibitors Low dose : 400 mg 400\text{ mg} 400 mg IV bolus at 30 mg/min 30\text{ mg/min} 30 mg/min followed by 480 mg 480\text{ mg} 480 mg infusion at 4 mg/min 4\text{ mg/min} 4 mg/min over 2 hours 2\text{ hours} 2 hours (for apixaban or rivaroxaban ≤ 10 mg \le 10\text{ mg} ≤ 10 mg , or last dose > 8 h > 8\text{ h} > 8 h ). High dose : 800 mg 800\text{ mg} 800 mg IV bolus followed by 960 mg 960\text{ mg} 960 mg infusion over 2 hours 2\text{ hours} 2 hours (rivaroxaban > 10 mg > 10\text{ mg} > 10 mg or apixaban > 5 mg > 5\text{ mg} > 5 mg taken within 8 hours 8\text{ hours} 8 hours ). If unavailable, administer 4F-PCC 50 U/kg 50\text{ U/kg} 50 U/kg or fixed dose 2000 U.

Unfractionated Heparin (UFH) Protamine Sulfate Positively charged alkaline peptide that neutralizes negatively charged heparin via stable salt formation 1 mg 1\text{ mg} 1 mg protamine per 100 U 100\text{ U} 100 U of heparin administered in preceding 2-3 hours (max single dose 50 mg 50\text{ mg} 50 mg ). Infuse slowly over 10 − 15 min 10 - 15\text{ min} 10 − 15 min to prevent severe hypotension, bradycardia, and anaphylaxis.

Low-Molecular-Weight Heparin (Enoxaparin) Protamine Sulfate (partial reversal) Binds and neutralizes anti-IIa activity ( 100 % 100\% 100% ); partially neutralizes anti-Xa activity ( 60 % − 75 % 60\% - 75\% 60% − 75% ) If enoxaparin given within 8 hours 8\text{ hours} 8 hours : 1 mg 1\text{ mg} 1 mg protamine per 1 mg 1\text{ mg} 1 mg enoxaparin . If given 8 − 12 hours 8 - 12\text{ hours} 8 − 12 hours prior: 0.5 mg 0.5\text{ mg} 0.5 mg protamine per 1 mg 1\text{ mg} 1 mg enoxaparin.