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Acquired Coagulation Protein Disorders |  |
| Most coagulation proteins are produced primarily in the liver. Therefore, liver disease characterized by necrosis, inflammation, neoplasia, or cirrhosis often is associated with decreased production of coagulation proteins, particularly Factors VII, IX, X, and XI. Because the various coagulation proteins have a relatively short half-life (4 hr to 2 days), mild to marked deficiencies can result secondary to severe hepatopathies. The APTT or PT (or both) are prolonged in 50-66% of
dogs with liver disease, meaning that the factor activity is <30% of normal. Coagulation tests are often performed before liver biopsy. Severe hepatic diseases can also lead to disseminated intravascular coagulation. Fibrinogen, an acute phase reactant, and von Willebrand’s factor, which is produced extrahepatically, can be increased in liver disease. |
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Ingestion of anticoagulant rodenticides by dogs and cats causes a coagulopathy owing to the lack of production of functional vitamin K-dependent factors (see
rodenticide poisoning,
Rodenticide Poisoning: Introduction). Inactive precursor coagulation Factors II, VII, IX, and X are still produced by the liver, but γ-carboxylation of the inactive precursors does not occur because the rodenticide inhibits the epoxide-reductase enzyme required for recycling of active vitamin K. There are 2 classes of rodenticides: the coumarin compounds (warfarin, coumafuryl, brodifacoum, and bromadiolone) and the indanedione compounds
(diphacinone, pindone, valone, and chlorophacinone). However, the half-life of the coumarins (up to 55 hr) is much shorter than that of the indanedione compounds (15-20 days). Affected animals may have hematoma formation (especially over pressure points) and bruising of superficial and deep tissues. Often, the animals do not bleed within the first 24 hr after ingestion of the toxin. The APTT, PT, and ACT are usually prolonged. Factor VII has the shortest half-life of the vitamin
K-dependent coagulation proteins; therefore, the PT is often abnormal before other tests and can be used to monitor response to treatment. Vitamin K1, 0.25-2.5 mg/kg, PO, for 4-6 days, is recommended for treatment of coumarin toxicity. Doses of vitamin K1 as high as 5 mg/kg, PO, for 3-6 wk, may be required for treatment of indanedione toxicity; however, these high doses should be administered cautiously because Heinz body anemia has been
reported in dogs given 4 mg/kg for 5 days. IV administration of vitamin Kl is not recommended because anaphylactic reactions can result. Administration of vitamin K3 is not useful. |
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Disseminated intravascular coagulation (DIC) is a syndrome characterized by massive activation and consumption of coagulation proteins, fibrinolytic proteins, and platelets. It is not a primary disease, but a disorder secondary to numerous triggering events such as bacterial, viral, rickettsial, protozoal, or parasitic diseases; heat stroke; burns; neoplasia; or severe trauma. In acute, fulminant DIC, the clinical presentation is uncontrolled hemorrhaging and the
inability to form a normal clot. Classically, all coagulation screening tests (ACT, APTT, PT, thrombin time) are prolonged, fibrin (or fibrinogen) degradation products are increased, and fibrinogen and platelet concentrations are decreased. Death is caused by extensive microthrombosis or circulatory failure, leading to single or multiple organ failure. If the animal survives the acute DIC event, a chronic form of DIC can exist. Compensatory production of coagulation proteins and
platelets by the liver and bone marrow, respectively, can alter the results of coagulation screening tests such that they may be within reference ranges or even shortened, and platelet concentrations may be normal. However, DIC can usually be identified by the presence of at least 3 abnormal coagulation test results. Horses, even in fulminant DIC, most often have hyperfibrinogenemia because their liver can produce much fibrinogen. Treatment should be directed toward correcting the
underlying problem. Supportive care is essential. Administration of balanced electrolyte solutions to maintain effective circulating volume is imperative. Administration of heparin is controversial and should be accompanied by administration of plasma to assure adequate antithrombin III activity. |
