Overview

• Acquired or hereditary defects that can affect any of the main functions of platelets, including procoagulant activity. Defects are divided in 2 categories: intrinsic and extrinsic (e.g., vWD).
• Affected animals typically have normal platelet counts but have spontaneous or excessive bleeding; mucosal bleeding is the most common sign.
• Thrombocytopenic animals with concurrent thrombocytopathia will bleed more excessively than expected for the platelet count.

Signalment

• Acquired defects are the most common thrombocytopathias seen in companion animals. They occur in all breeds and at all ages.
• Hereditary platelet function defects may be diagnosed at all ages but may first appear in young animals when excessive bleeding occurs with loss of deciduous teeth.
• Hereditary defects are rare disorders that have been described in the following breeds/species:
  • Type I Glanzmann thrombasthenia-otter hound and Great Pyrenees
  • Storage pool disease-Chediak-Higashi syndrome-Persian cat; delta-granule-American cocker spaniel; cyclic hematopoiesis-grey collie
  • Thrombocytopathia (CalDAG-GEFI deficiency) -basset hound, spitz, and Landseer
  • Scott syndrome-German shepherd
  • P2Y12 (ADP) receptor mutation-Greater Swiss mountain dog

Signs

• Often mild spontaneous muco-cutaneous bleeding, such as epistaxis, petecchiation, and gingival bleeding.
• Prolonged bleeding in some animals during or following diagnostic or surgical procedures.
• In Scott syndrome, postoperative hemorrhage is the most common sign.

Causes & Risk Factors

CBC/Biochemistry/Urinalysis

• Anemia, if bleeding is severe; regenerative or nonregenerative.
• Platelet counts typically normal in dogs with inherited thrombocytopathies, but low counts with bizarre and giant platelets seen in some.
• Biochemical profile-no specific changes.

Other Laboratory Tests

• Platelet function analyzer-100 and vWF by immune assay-in animals suspected of vWD.
• Platelet function testing-in specialized laboratories. The most common tests are platelet aggregation and flow cytometry.
• Coagulation tests (thromboelastography, PT, and APTT)-to eliminate coagulopathy as a cause of hemorrhage; APTT may be prolonged in some animals with von Willebrand disease.
• Genetic testing of carrier animals.

Diagnostic Procedures

Mucosal bleeding time-to confirm platelet function defect; normal buccal mucosal bleeding time measured using a spring-loaded lancet that makes an incision 5 mm long by 1 mm deep (Triplett, Helena Laboratories, Beaumont, TX) is less than 4–5 minutes in dogs and less than 2–3 minutes in cats.

Drug(s)

• Desmopressin acetate (DDAVP) (1 µg/kg SC or IV diluted in 20 mL saline administered over 10 minutes) to dogs with von Willebrand disease during a bleeding episode (if effective, effect lasts 2–3 hours).
• Desmopressin (3 µg/kg SC) improves bleeding time in dogs with thrombocytopathia due to aspirin and liver disease. It is beneficial in many thrombocytopathies in humans, so consider using in dogs with other thrombocytopathias.
• Give desmopressin to donor 30 minutes before collection of blood for transfusion to dogs with von Willebrand disease or thrombocytopathia.

See Also

• Thrombocytopenia
• Von Willebrand Disease

Abbreviations

• ADP = adenosine diphosphate
• APTT = activated partial thromboplastin time
• DDAVP = 1-desamino-8-d-arginine vasopressin
• NSAID = nonsteroidal anti-inflammatory drug
• PT = prothrombin time
• vWD = von Willebrand disease
• vWF = von Willebrand factor