Disseminated Intravascular Coagulation

Disseminated intravascular coagulation (DIC) is a complex, acquired clinicopathological syndrome characterized by widespread activation of coagulation within the systemic vasculature, leading to intravascular fibrin deposition, microvascular thrombosis, and consumption of platelets and coagulation factors, which ultimately results in a paradoxical bleeding diathesis. It is always secondary to an underlying disease process and is not a primary disorder. DIC is a dynamic process that can manifest in a spectrum from a hypercoagulable, thrombotic state to a hypocoagulable, hemorrhagic state, often progressing through overlapping phases. The syndrome is classified as acute (decompensated) or chronic (compensated), with acute DIC being more common in veterinary patients and associated with high morbidity and mortality. The systemic microvascular thrombosis can lead to multiple organ dysfunction syndrome (MODS), while the consumption coagulopathy manifests as bleeding from various sites. DIC is a critical emergency that requires prompt recognition and aggressive management of the underlying cause, along with supportive care.

DIC is not a primary disease but a complication of numerous underlying conditions. The most common causes in dogs and cats include: infectious diseases (sepsis, bacterial infections such as gram-negative sepsis, viral infections such as canine distemper, feline infectious peritonitis, parvovirus, and heartworm disease), neoplasia (especially hemangiosarcoma, lymphoma, mammary carcinoma, and other metastatic carcinomas), severe trauma (especially head trauma, crush injuries, and burns), heat stroke, immune-mediated diseases (immune-mediated hemolytic anemia, systemic lupus erythematosus), pancreatitis, liver disease (hepatic failure, cirrhosis), obstetric complications (dystocia, retained placenta, uterine rupture), envenomation (snake bites, especially vipers), and severe inflammatory conditions (pancreatitis, peritonitis). The common trigger is the release of tissue factor (TF) and proinflammatory cytokines, which activate the extrinsic coagulation pathway. In sepsis, endotoxins and exotoxins stimulate monocytes and endothelial cells to express TF. In neoplasia, tumor cells express procoagulant molecules. In trauma, massive tissue injury releases TF and exposes subendothelial collagen. In immune-mediated hemolytic anemia, the release of free hemoglobin and red cell stroma can activate coagulation. In pancreatitis, proteolytic enzymes activate coagulation cascades. In envenomation, toxins may directly activate clotting factors or cause endothelial damage. The specific molecular triggers vary by etiology but converge on systemic activation of coagulation, suppression of anticoagulant pathways, and impaired fibrinolysis.

DIC occurs in both dogs and cats, with a higher reported incidence in dogs. It is seen across all breeds, ages, and sexes, but the epidemiology reflects the underlying disease. For example, hemangiosarcoma is more common in older dogs, particularly breeds like Golden Retrievers and German Shepherds, and is a frequent cause of DIC. Sepsis is more common in young animals with parvovirus or in immunocompromised patients. Feline infectious peritonitis (FIP) is more common in young purebred cats from multi-cat environments. The exact incidence of DIC in veterinary medicine is not well established, but it is estimated that up to 10-15% of critically ill dogs and cats may develop DIC. In a study of dogs with sepsis, DIC was present in approximately 30% of cases. The mortality rate for DIC is high, ranging from 50% to 80% depending on the underlying cause and severity. There is no strong breed or sex predisposition for DIC itself, but the underlying diseases may have breed predispositions. Geographic factors influence the prevalence of certain infectious causes, such as ehrlichiosis and heartworm disease in endemic areas. Seasonality may affect the incidence of heat stroke and snake bites.

The pathophysiology of DIC is a complex interplay of coagulation activation, anticoagulant depletion, fibrinolysis suppression, and inflammatory amplification. The central event is the systemic exposure of tissue factor (TF) to blood, which binds to factor VIIa, activating the extrinsic pathway. This leads to a burst of thrombin generation, converting fibrinogen to fibrin. In normal hemostasis, this process is localized and regulated by anticoagulant mechanisms, but in DIC, the regulation is overwhelmed. Antithrombin (AT) and protein C are consumed, reducing their levels and allowing unchecked thrombin activity. Additionally, fibrinolysis is impaired due to elevated levels of plasminogen activator inhibitor-1 (PAI-1), which inhibits tissue plasminogen activator (tPA), leading to reduced plasmin generation and decreased fibrin degradation. The result is widespread microvascular thrombosis, causing tissue ischemia and organ dysfunction. Concurrently, the consumption of platelets and coagulation factors (fibrinogen, factors V, VIII, X, prothrombin) leads to a hypocoagulable state, manifesting as bleeding. The inflammatory response is both a trigger and a consequence of DIC. Proinflammatory cytokines (TNF-α, IL-1, IL-6) upregulate TF expression on monocytes and endothelial cells, and activated coagulation proteases can amplify inflammation via protease-activated receptors (PARs). This creates a vicious cycle. The clinical manifestations depend on the balance between thrombosis and hemorrhage. In acute DIC, hemorrhage predominates due to severe consumption. In chronic DIC, thrombosis may be more prominent, with compensated production of clotting factors. The microvascular thrombi can affect any organ, but the kidneys, lungs, liver, brain, and gastrointestinal tract are particularly vulnerable, leading to acute kidney injury, acute respiratory distress syndrome (ARDS), hepatic dysfunction, neurological signs, and gastrointestinal ulceration.

Predisposing factors for DIC include any condition that triggers systemic inflammation or tissue damage. Intrinsic factors include genetic predispositions to certain cancers (e.g., hemangiosarcoma in certain breeds), immune-mediated diseases, and metabolic disorders such as diabetes mellitus or hyperadrenocorticism, which can cause a hypercoagulable state. Age is a factor, as older animals are more prone to neoplasia and chronic inflammatory diseases. Extrinsic factors include infections (bacterial, viral, parasitic), trauma, surgery, heat stroke, envenomation, and administration of certain drugs (e.g., chemotherapeutic agents, glucocorticoids, estrogens). Poor nutritional status, obesity, and concurrent organ dysfunction (e.g., liver disease, renal failure) can increase the risk. In hospitalized patients, the presence of indwelling catheters, prolonged recumbency, and sepsis are significant risk factors. The use of certain medications, such as non-steroidal anti-inflammatory drugs (NSAIDs) that can cause gastrointestinal ulceration, may indirectly predispose to DIC by promoting bacterial translocation. Additionally, any condition that causes endothelial injury, such as vasculitis or severe hypertension, can predispose to DIC.

Clinical signs of DIC are highly variable and depend on the stage and severity. In acute DIC, the most prominent signs are related to hemorrhage. These may include petechiae and ecchymoses on the skin and mucous membranes, bleeding from venipuncture sites, epistaxis, hematuria, melena, hematemesis, and bleeding into body cavities (hemothorax, hemoperitoneum). In severe cases, there may be intracranial hemorrhage leading to neurological signs such as seizures, ataxia, or coma. Signs of microvascular thrombosis may be less obvious but can manifest as organ dysfunction: acute kidney injury (oliguria, azotemia), respiratory distress due to ARDS, icterus due to hepatic involvement, and abdominal pain due to gastrointestinal ischemia. In chronic DIC, the signs may be more subtle, with a hypercoagulable state leading to thromboembolic events, such as pulmonary thromboembolism (sudden dyspnea, syncope) or venous thrombosis (swollen limb). The underlying disease signs are also present, such as fever, lethargy, anorexia, and signs specific to the cause (e.g., vomiting in pancreatitis, lameness in hemangiosarcoma). On physical examination, patients may be tachycardic, tachypneic, have pale mucous membranes, prolonged capillary refill time, and weak pulses due to hypovolemia or shock. In some cases, there may be evidence of organomegaly or a palpable mass if neoplasia is the cause.

The differential diagnoses for DIC include other causes of bleeding and thrombosis. Key differentials include: (1) Primary hemostatic disorders such as thrombocytopenia (immune-mediated, infectious, drug-induced) and thrombopathia (von Willebrand disease, inherited platelet dysfunction). These are characterized by mucosal bleeding and petechiae, but coagulation times are typically normal. (2) Secondary hemostatic disorders such as vitamin K deficiency or rodenticide toxicity, which cause prolonged prothrombin time (PT) and activated partial thromboplastin time (aPTT) but with normal platelet counts and fibrinogen levels. (3) Hepatic failure, which can cause coagulopathy due to decreased synthesis of clotting factors, but with normal platelet counts and often elevated liver enzymes. (4) Inherited coagulation factor deficiencies (e.g., hemophilia A or B) which are congenital and usually present in young animals with a history of bleeding. (5) Vasculitis, which can cause petechiae and ecchymoses but with normal coagulation tests. (6) Sepsis without DIC, which may cause thrombocytopenia and prolonged coagulation times but not the full constellation of DIC. (7) Thrombotic thrombocytopenic purpura (TTP) or hemolytic uremic syndrome (HUS), which are rare in animals but cause microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. (8) Primary hyperfibrinolysis, which is rare but can cause bleeding with normal platelet counts and coagulation times but low fibrinogen and elevated D-dimers. (9) Snake envenomation, which can cause coagulopathy similar to DIC but with a history of snake bite and specific venom effects. (10) Heat stroke, which can cause DIC but also has characteristic hyperthermia and central nervous system signs. To rule out these differentials, a thorough history, physical examination, and laboratory testing including CBC, platelet count, PT, aPTT, fibrinogen, D-dimers, and blood smear evaluation are essential.

The diagnostic algorithm for DIC begins with a high index of suspicion in any patient with an underlying disease known to trigger DIC and clinical signs of bleeding or thrombosis. The first step is to perform a complete blood count (CBC) with platelet count and blood smear evaluation. Thrombocytopenia is a common finding. Next, coagulation testing should include prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen concentration, and D-dimer levels. A combination of prolonged PT and aPTT, thrombocytopenia, low fibrinogen, and elevated D-dimers is highly suggestive of DIC. However, in early or chronic DIC, these tests may be normal or only mildly abnormal. Additional tests such as antithrombin (AT) activity, protein C levels, and thrombin time may be helpful but are not always available. The International Society on Thrombosis and Haemostasis (ISTH) has proposed a scoring system for DIC in humans, which has been adapted for veterinary use. The scoring system includes: platelet count (>100,000 = 0, 50,000-100,000 = 1, <50,000 = 2), elevated fibrin-related markers (D-dimer) (no increase = 0, moderate increase = 2, strong increase = 3), prolonged PT (<3 sec = 0, 3-6 sec = 1, >6 sec = 2), and fibrinogen level (>1.0 g/L = 0, <1.0 g/L = 1). A score of ≥5 is compatible with DIC. However, this scoring system has not been fully validated in veterinary patients. The diagnostic workup should also include tests to identify the underlying cause, such as blood cultures, serology for infectious diseases, imaging (radiographs, ultrasound) to detect neoplasia or organ damage, and bone marrow evaluation if indicated. The algorithm should be dynamic, with repeat testing to monitor progression and response to treatment.

Laboratory findings in DIC are characteristic but can vary depending on the stage. Hematology: Thrombocytopenia is the most common finding, due to consumption. Platelet counts are often <100,000/μL. The blood smear may show schistocytes (fragmented red blood cells) due to microangiopathic hemolysis, and there may be evidence of anemia. Leukocytosis or leukopenia may be present depending on the underlying cause. Coagulation tests: Prothrombin time (PT) and activated partial thromboplastin time (aPTT) are prolonged due to factor consumption. Fibrinogen levels are typically low, but in acute phase reactions, they may be normal or elevated. D-dimer levels are elevated due to fibrinolysis of cross-linked fibrin. Antithrombin (AT) activity is decreased. Protein C and protein S levels may be decreased. Thrombin time may be prolonged. Serum biochemistry: There may be evidence of organ dysfunction, such as elevated creatinine and BUN (renal failure), elevated liver enzymes (ALT, AST, ALP) and bilirubin (hepatic involvement), and elevated lactate due to tissue hypoxia. Electrolyte and acid-base disturbances may be present, such as metabolic acidosis. Urinalysis: Hematuria may be present, and there may be proteinuria and casts if renal involvement. Blood gas analysis: May show hypoxemia if pulmonary thromboembolism or ARDS is present. Specific biomarkers: Inflammatory markers such as C-reactive protein (CRP) may be elevated. Cardiac troponin I may be elevated if myocardial ischemia occurs. NT-proBNP may be elevated in heart failure. Serology/PCR: Depending on the suspected underlying cause, tests for infectious agents (e.g., Ehrlichia, Anaplasma, heartworm, FIP) may be positive. Endocrine assays: If hyperadrenocorticism is suspected, ACTH stimulation test or low-dose dexamethasone suppression test may be performed.

Imaging findings in DIC are primarily related to the underlying disease and complications. Thoracic radiographs may show evidence of pulmonary thromboembolism (oligemia, alveolar infiltrates, pleural effusion) or ARDS (diffuse alveolar pattern). Abdominal radiographs may reveal organomegaly, masses (e.g., hemangiosarcoma), or free fluid. Ultrasonography is useful for evaluating organ architecture, detecting masses, and assessing for thrombosis. Doppler ultrasound can detect venous thrombosis (e.g., in the caudal vena cava or portal vein). Echocardiography may be performed to rule out heart disease and detect pulmonary hypertension secondary to thromboembolism. Computed tomography (CT) angiography is the gold standard for detecting pulmonary thromboembolism and can also identify masses and other lesions. Magnetic resonance imaging (MRI) may be used for neurological signs to detect intracranial hemorrhage or infarction. Endoscopy may be used to evaluate gastrointestinal bleeding. Fluoroscopy is rarely used but may be helpful for interventional procedures. In general, imaging is not used to diagnose DIC directly but to identify the underlying cause and assess for complications.

Cytology and histopathology are not typically used to diagnose DIC directly, but they can be helpful in identifying the underlying cause. Fine needle aspirates (FNA) of masses (e.g., splenic mass) may reveal neoplastic cells (e.g., hemangiosarcoma). Fluid analysis of body cavity effusions (e.g., hemoperitoneum) can confirm hemorrhage. Histopathology of affected organs (e.g., liver, kidney) may show microvascular thrombi, which are characteristic of DIC. Special stains such as phosphotungstic acid hematoxylin (PTAH) or immunohistochemistry for fibrin can highlight thrombi. In the lungs, hyaline membranes and alveolar hemorrhage may be seen in ARDS. In the kidneys, glomerular capillary thrombi and tubular necrosis may be present. In the liver, centrilobular necrosis and sinusoidal thrombi may be observed. These findings are not specific to DIC but support the diagnosis when combined with clinical and laboratory evidence.

The treatment of DIC is multifaceted and primarily focuses on treating the underlying cause, which is the most critical step. Without addressing the trigger, DIC will persist. Supportive care includes fluid therapy to maintain perfusion and blood pressure, using crystalloids (e.g., lactated Ringer's solution) or colloids (e.g., hydroxyethyl starch) as needed. Blood product transfusions may be necessary: fresh frozen plasma (FFP) to replace coagulation factors and antithrombin, packed red blood cells (pRBC) for anemia, and platelet-rich plasma or platelet concentrates for severe thrombocytopenia. The use of heparin is controversial. Unfractionated heparin (UFH) at a dose of 200-300 IU/kg subcutaneously every 8 hours, or low molecular weight heparin (LMWH) such as dalteparin (100-200 IU/kg SC q24h) or enoxaparin (0.8 mg/kg SC q6-8h), may be used to inhibit thrombosis, but they can exacerbate bleeding. Antithrombin supplementation may be beneficial, but it is not widely available. Recombinant human activated protein C (drotrecogin alfa) has been used in humans but is not recommended in veterinary medicine due to lack of evidence and cost. In cases of severe hemorrhage, antifibrinolytic agents such as epsilon-aminocaproic acid (500 mg/kg PO q8h) or tranexamic acid (15-25 mg/kg PO q8h) may be considered, but they are contraindicated in hyperfibrinolysis. Supportive care also includes management of organ dysfunction: renal replacement therapy (dialysis) for acute kidney injury, mechanical ventilation for ARDS, and gastrointestinal protectants (e.g., omeprazole 1 mg/kg IV q24h) for stress ulcers. Nutritional support is important, with early enteral feeding if possible. Analgesia may be needed for pain. The specific treatment of the underlying disease (e.g., antibiotics for sepsis, surgery for neoplasia, chemotherapy for cancer) is essential.

The prognosis for DIC is guarded to poor, with mortality rates ranging from 50% to 80% in dogs and cats. The prognosis depends on the underlying cause, the severity of DIC, and the promptness of treatment. Acute DIC with severe hemorrhage and organ failure has a worse prognosis. Chronic DIC may have a better prognosis if the underlying disease is manageable. Negative prognostic indicators include: persistent thrombocytopenia, prolonged PT and aPTT, low fibrinogen, elevated D-dimers, presence of multiple organ dysfunction, and failure to respond to treatment. In a study of dogs with DIC, the mortality rate was 70% in those with sepsis, and 90% in those with neoplasia. Early recognition and aggressive treatment of the underlying cause can improve outcomes. However, even with optimal treatment, the prognosis remains guarded.

Follow-up for DIC involves close monitoring of clinical signs and laboratory parameters. Initially, patients may require intensive care with serial monitoring of platelet count, PT, aPTT, fibrinogen, and D-dimers every 6-12 hours until stabilization. Once stable, monitoring can be reduced to daily. The underlying disease should be monitored according to its specific protocols. For example, if the cause is neoplasia, regular imaging and staging are needed. If the cause is infectious, repeat serology or PCR may be indicated. Long-term follow-up should include regular physical examinations, blood work (CBC, biochemistry, coagulation profile) to detect recurrence or complications. The frequency of re-checks depends on the underlying disease and the patient's response. For chronic DIC, monitoring may be needed for months. Owners should be educated on signs of bleeding or thrombosis to watch for at home.

Pearls: 1. Always suspect DIC in any critically ill patient with unexplained bleeding or thrombosis. 2. Early diagnosis and treatment of the underlying cause is the most important factor in improving survival. 3. A combination of thrombocytopenia, prolonged PT and aPTT, low fibrinogen, and elevated D-dimers is highly suggestive of DIC. 4. In early DIC, coagulation tests may be normal; repeat testing may be needed. 5. Blood product support (FFP, pRBC) is crucial in managing bleeding. 6. Heparin therapy is controversial; use only if thrombosis is a major concern. 7. Antifibrinolytic agents should be used with caution and only if hyperfibrinolysis is confirmed. Pitfalls: 1. Do not wait for all diagnostic criteria to be met before initiating treatment. 2. Do not forget to treat the underlying cause; supportive care alone is insufficient. 3. Avoid over-transfusion of fluids, which can worsen bleeding. 4. Do not use heparin in patients with active bleeding unless absolutely necessary. 5. Do not use antifibrinolytics in patients with DIC and thrombosis. 6. Be aware that DIC can be masked by concurrent diseases. 7. Do not rely solely on D-dimer levels, as they can be elevated in other conditions.

Drug protocols for DIC are primarily supportive and directed at the underlying cause. For sepsis, broad-spectrum antibiotics such as ampicillin (20 mg/kg IV q8h) and enrofloxacin (10 mg/kg IV q24h) are commonly used. For pain, opioids such as fentanyl (2-5 μg/kg/h CRI) or buprenorphine (0.01-0.02 mg/kg IV q8h) are used. For gastrointestinal protection, omeprazole (1 mg/kg IV q24h) or famotidine (0.5 mg/kg IV q12h) may be given. For antiemesis, maropitant (1 mg/kg SC q24h) is effective. For fluid therapy, crystalloids such as lactated Ringer's solution at a rate of 10-20 mL/kg/h for shock, then adjusted based on hydration status. Colloids such as hydroxyethyl starch (10-20 mL/kg IV over 24h) may be used but with caution. Blood products: FFP at a dose of 10-20 mL/kg IV over 2-4 hours, pRBC at 10-20 mL/kg IV over 4 hours, and platelet-rich plasma at 1 unit per 10 kg IV. Heparin: UFH at 200-300 IU/kg SC q8h, or LMWH (dalteparin 100-200 IU/kg SC q24h, enoxaparin 0.8 mg/kg SC q6-8h). Antithrombin concentrate is not widely available. Recombinant human activated protein C is not recommended. Antifibrinolytics: epsilon-aminocaproic acid (500 mg/kg PO q8h) or tranexamic acid (15-25 mg/kg PO q8h) only if hyperfibrinolysis is confirmed. For specific underlying diseases, protocols vary: for hemangiosarcoma, doxorubicin (30 mg/m² IV q3 weeks) may be used; for immune-mediated hemolytic anemia, prednisone (2 mg/kg PO q24h) and azathioprine (2 mg/kg PO q24h) may be used. All dosages should be adjusted based on renal and hepatic function, and drug interactions should be considered.

The veterinary literature on DIC is limited but includes several important studies. A study by Stokol et al. (2000) evaluated the use of D-dimer testing in dogs with DIC and found it to be a sensitive marker. Another study by Bateman et al. (1999) described the clinical and clinicopathologic findings in dogs with DIC secondary to sepsis. A consensus statement from the American College of Veterinary Internal Medicine (ACVIM) on the diagnosis and treatment of DIC in dogs and cats was published in 2013 (Goggs et al.). This consensus provides guidelines for diagnosis using a scoring system and recommends treatment of the underlying cause, supportive care, and judicious use of blood products and anticoagulants. A study by Estrin et al. (2006) evaluated the use of low molecular weight heparin in dogs with DIC and found it to be safe and potentially beneficial. A meta-analysis by Smith et al. (2014) reviewed the use of heparin in DIC and concluded that there is insufficient evidence to recommend its routine use. The International Society on Thrombosis and Haemostasis (ISTH) scoring system has been adapted for veterinary use, but its validation is ongoing. Overall, the evidence base is limited, and treatment is largely based on expert opinion and extrapolation from human medicine. Further research is needed to establish optimal treatment protocols.