NAVLE Multisystemic

Equine Disseminated Intravascular Coagulation Study Guide

📅 March 28, 2026 ⏱ 25 min read

Overview and Clinical Importance

Disseminated intravascular coagulation (DIC) is a complex, life-threatening clinicopathologic syndrome characterized by widespread systemic activation of the coagulation cascade, resulting in microvascular thrombosis and subsequent consumption of platelets and coagulation factors. In horses, DIC is always a secondary condition triggered by an underlying primary disease, most commonly gastrointestinal disorders (colic, colitis, strangulating lesions), sepsis, systemic inflammatory response syndrome (SIRS), and endotoxemia.

DIC represents a dynamic continuum ranging from a hypercoagulable (prothrombotic) state with microvascular thrombosis to a hypocoagulable (hemorrhagic) state characterized by consumption of clotting factors and bleeding. Understanding this pathophysiologic spectrum is critical for diagnosis and treatment.

High-YieldDIC is NEVER a primary disease. Always identify and treat the underlying cause. The most common triggers in horses are gastrointestinal disorders (colic, colitis, enteritis) and sepsis/endotoxemia. Laminitis is a devastating complication of equine DIC and should be anticipated in all affected horses.

Pathway	Key Factors	Test Used
Extrinsic	Tissue Factor (TF), Factor VII	Prothrombin Time (PT)
Intrinsic	Factors XII, XI, IX, VIII	aPTT
Common	Factors X, V, II (Prothrombin), I (Fibrinogen)	PT and aPTT both affected

Pathophysiology

The Coagulation Cascade

Understanding the normal coagulation cascade is essential for comprehending DIC pathophysiology. Secondary hemostasis involves two pathways (extrinsic and intrinsic) that converge on a common pathway, ultimately generating thrombin, which converts fibrinogen to fibrin.

Key Components of the Coagulation Cascade

Mechanism of DIC Development

DIC is initiated by inappropriate, uncontrolled activation of hemostasis. The process can be divided into phases:

Initiation Phase

The primary trigger is exposure of blood to tissue factor (TF). In horses, this commonly occurs through: endotoxin (LPS) stimulating monocytes to express TF, widespread endothelial injury exposing subendothelial TF, release of TF from damaged tissues (e.g., necrotic bowel), and cancer cells expressing TF.

Amplification Phase

TF-Factor VIIa complex activates Factor X, generating small amounts of thrombin. Thrombin then amplifies its own production by activating Factors V, VIII, and XI. This creates a positive feedback loop leading to massive ("explosive") thrombin generation.

Propagation and Dissemination

When thrombin generation overwhelms natural anticoagulants (antithrombin, protein C, tissue factor pathway inhibitor), hemostasis loses spatial localization. Microvascular thrombi form throughout the body, leading to tissue ischemia and organ dysfunction.

Consumption and Hemorrhage

As platelets and coagulation factors are consumed in widespread clot formation, the patient transitions from a hypercoagulable to a hypocoagulable state. Secondary fibrinolysis breaks down clots, generating D-dimers and fibrin degradation products (FDPs).

High-YieldThe key concept is that DIC exists on a continuum. Early DIC is characterized by hypercoagulability with microthrombosis ("non-overt" or thrombotic DIC). Late DIC shows consumption with bleeding ("overt" or hemorrhagic DIC). Horses more commonly present with the hypercoagulable/thrombotic phenotype, whereas dogs often show hemorrhagic DIC.

Natural Anticoagulants and Their Depletion

Anticoagulant	Function	Clinical Significance in DIC
Antithrombin (AT)	Inhibits thrombin, FXa, FIXa, FXIa, FXIIa. Activity enhanced 1000-fold by heparin.	Consumed during DIC. AT less than 70% = heparin therapy ineffective. Measure before anticoagulation.
Protein C	When activated by thrombin-thrombomodulin complex, inactivates FVa and FVIIIa	Decreased in horses with colic and endotoxemia. Associated with increased mortality.
TFPI	Tissue Factor Pathway Inhibitor. Inhibits TF-FVIIa-FXa complex.	Overwhelmed in DIC. Cannot contain TF-initiated coagulation.

Etiology: Primary Diseases Causing DIC in Horses

DIC is always secondary to an underlying disease. The most common triggers in horses involve systemic inflammation, endotoxemia, or tissue damage.

NAVLE TipOn NAVLE, when you see a horse with colic (especially strangulating lesions or colitis) combined with petechiae, prolonged bleeding from venipuncture sites, or laminitis, think DIC immediately. Septic neonatal foals are also highly susceptible to DIC.

Category	Specific Conditions	Mechanism
GI Disorders (Most Common)	Strangulating colic (small intestinal volvulus, large colon torsion) Enterocolitis/Colitis Duodenitis-proximal jejunitis Peritonitis	Endotoxin release from compromised gut barrier, tissue necrosis, SIRS
Sepsis	Neonatal septicemia Pleuropneumonia Metritis Endocarditis	Endotoxin/LPS activates monocyte TF expression, cytokine storm (TNF-alpha, IL-1, IL-6)
Neoplasia	Disseminated neoplasia, Hemangiosarcoma, Lymphoma	Tumor cells express TF, release procoagulant extracellular vesicles
Other	Severe hemorrhage/massive transfusion Anaphylaxis Drug reactions Retained fetal membranes	Tissue injury, immune-mediated endothelial damage, hypoxic injury

Clinical Signs

Clinical signs of DIC are highly variable and depend on: the underlying primary disease, the balance between thrombosis and hemorrhage, and which organs are affected by microvascular thrombosis.

Signs Related to Primary Disease

DIC never presents alone. Clinical signs of the underlying condition will dominate initially: colic signs (pawing, rolling, looking at flank), fever, tachycardia, tachypnea, depression, and signs of sepsis or SIRS.

Hemorrhagic Manifestations

Petechiae and ecchymoses: Small (petechiae less than 3mm) or larger (ecchymoses) red/purple spots on mucous membranes (gums, conjunctivae, vulva)
Prolonged bleeding: From venipuncture sites, surgical wounds, or minor trauma
Epistaxis: Bleeding from the nostrils
Melena: Dark, tarry feces indicating GI hemorrhage
Hematuria: Blood in urine
Hematoma formation: Especially following venipuncture or catheter placement

Thrombotic Manifestations

Laminitis: Microvascular thrombosis in the laminae leads to ischemia and laminar failure. This is one of the most devastating complications.
Jugular thrombophlebitis: Clot formation in the jugular vein, often at catheter sites
Organ dysfunction: Signs related to ischemic injury of kidneys (oliguria, azotemia), liver, lungs (respiratory distress), or intestines (colic signs)
Cold extremities: Poor peripheral perfusion due to microvascular thrombosis

High-YieldIn horses, laminitis is considered part of the multiple organ dysfunction syndrome (MODS) criteria. Always monitor for laminitis in any horse with SIRS, sepsis, or DIC. Check digital pulses, hoof wall temperature, and monitor for shifting weight or reluctance to move. Early recognition is critical for aggressive preventive treatment.

Parameter	Normal Range (Horse)	DIC Finding	Clinical Significance
Platelet Count	100,000-350,000/uL	Decreased (Thrombocytopenia)	Consumption in microvascular thrombi
PT (Prothrombin Time)	Less than 15 seconds	Prolonged (greater than 15 sec)	Consumption of extrinsic/common pathway factors
aPTT	Less than 65 seconds	Prolonged (greater than 65 sec)	Consumption of intrinsic/common pathway factors. More sensitive than PT in horses.
Fibrinogen	200-400 mg/dL	Decreased (hypofibrinogenemia) OR elevated initially	Acute phase protein (may increase in inflammation), but consumed in overt DIC
D-dimer	Less than 500 ng/mL	ELEVATED (greater than 1000 ng/mL diagnostic)	Indicates fibrinolysis of cross-linked fibrin. Highly specific for intravascular clotting.
Antithrombin (AT)	Greater than 140%	Decreased (less than 140%)	Consumption in DIC. Less than 70% = heparin therapy will be ineffective.

Diagnosis

Diagnosis of DIC requires integration of clinical findings with laboratory abnormalities. There is no single pathognomonic test. Traditionally, DIC is diagnosed when at least 3 of the following hemostatic parameters are abnormal:

Laboratory Diagnostic Criteria

Exam Focus: D-dimer is highly elevated in DIC and is one of the most sensitive markers of intravascular coagulation and fibrinolysis. In horses with colic, D-dimer greater than 1000 ng/mL is strongly associated with DIC. However, D-dimer alone is not diagnostic and must be interpreted with other parameters. For NAVLE, remember that the aPTT is often more sensitive than PT for detecting DIC in horses.

Non-Overt (Subclinical) vs. Overt (Clinical) DIC

Additional Diagnostic Findings

Schistocytes: Fragmented RBCs (helmet cells) on blood smear from microangiopathic hemolytic anemia (MAHA) - RBCs sheared by fibrin strands in microvessels
FDPs (Fibrin Degradation Products): Elevated, though less specific than D-dimer
TAT (Thrombin-Antithrombin complexes): Elevated; indicates ongoing thrombin generation
Evidence of underlying disease: Leukocytosis/leukopenia, band neutrophils, toxic changes, elevated lactate, azotemia

Non-Overt (Compensated/Subclinical) DIC	Overt (Decompensated/Clinical) DIC
No overt clinical signs of coagulopathy PT and aPTT may be normal or mildly prolonged D-dimer elevated AT activity decreased Hypercoagulable state; microthrombosis occurring Diagnosis requires 3 or more abnormalities	Obvious clinical hemorrhage or thrombosis PT and aPTT significantly prolonged D-dimer markedly elevated Fibrinogen decreased (consumption) Thrombocytopenia present Hypocoagulable state; consumption of factors

Treatment

The principal goal of DIC therapy is to identify and treat the underlying cause. Treatment of DIC itself is supportive and aimed at breaking the cycle of coagulation activation.

Treatment Approach Summary

High-YieldHeparin requires adequate antithrombin to be effective. If AT activity is less than 70%, plasma transfusion is needed before or with heparin therapy. Mini-dose heparin (5-10 IU/kg) can be added to plasma 30 minutes before administration. Do NOT give heparin to actively bleeding patients - this will worsen hemorrhage.

Treatment Category	Specific Interventions	Notes
Treat Primary Disease	Surgery for strangulating colic Antimicrobials for sepsis Uterine lavage for metritis	CRITICAL. Without treating the inciting cause, DIC cannot be resolved.
Fluid Therapy	Crystalloids (LRS, Plasmalyte) Colloids (caution: may affect hemostasis)	Maintain tissue perfusion. Avoid excessive hetastarch if bleeding present.
Plasma Transfusion	Fresh Frozen Plasma (FFP) Dose: 10-20 mL/kg IV	Provides coagulation factors, antithrombin, protein C and S. Indicated if AT less than 70% or if actively bleeding.
Heparin Therapy	UFH: 40-80 IU/kg SQ q8-12h LMWH (Enoxaparin): 40-80 IU/kg SQ q24h Mini-dose: 5-10 IU/kg added to plasma	Enhances antithrombin activity. ONLY effective if AT greater than 70%. Give with plasma if AT low. Contraindicated if actively bleeding.
Anti-inflammatory	Flunixin meglumine: 1.1 mg/kg IV q12h (or 0.25 mg/kg q8h) Pentoxifylline: 8.5 mg/kg IV q12h	Anti-endotoxin effects. Pentoxifylline has anti-inflammatory and rheologic benefits.
Anti-platelet Therapy	Aspirin: 10-20 mg/kg PO or PR q48h Clopidogrel: 2 mg/kg PO q24h (after 4 mg/kg loading dose)	Inhibits platelet aggregation. Consider for laminitis prevention. May have inconsistent effects in inflamed horses.
Laminitis Prevention	Cryotherapy (ice boots) for 48-72 hours Frog support Anti-platelet therapy	Critical component of SIRS/DIC management. Continuous digital hypothermia reduces laminitis incidence.

Complications and Prognosis

Multiple Organ Dysfunction Syndrome (MODS)

MODS is defined as dysfunction of 2 or more organ systems. In horses, this includes:

Laminitis (laminar failure due to microvascular thrombosis)
Hemostatic dysfunction (DIC itself)
Renal dysfunction (azotemia, oliguria)
Respiratory dysfunction (tachypnea, hypoxemia)
Hepatic dysfunction (hyperbilirubinemia, elevated liver enzymes)
Neurological dysfunction (depression, obtundation)
Cardiovascular dysfunction (hypotension, poor perfusion)

Prognosis

Prognosis for horses with DIC is generally guarded to poor, and depends heavily on:

The severity and treatability of the underlying disease
How early DIC is recognized and treated
Whether the patient is in non-overt (better prognosis) vs. overt (worse prognosis) DIC
Development of MODS complications, especially laminitis
Response to therapy

Historically, survival rates in horses with DIC secondary to colic ranged from approximately 34% in one study. Foals with sepsis-associated DIC have survival rates of 26-86% depending on severity and promptness of treatment. The development of laminitis significantly worsens prognosis.

NAVLE TipIt is NOT recommended to anesthetize a horse in DIC as they can become profoundly hypotensive during anesthesia. If surgery is absolutely required, be prepared for severe hemodynamic instability and consider aggressive plasma and blood product support perioperatively.

Memory Aid

DIC = "Death Is Coming" (reflects the poor prognosis)

DIC Diagnostic Criteria - Remember "3 of 6":

Platelets decreased
PT prolonged
aPTT prolonged
Fibrinogen decreased
D-dimer increased
Antithrombin decreased

Heparin Needs "AT" = Antithrombin must be adequate (greater than 70%) for heparin to work!

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