Asymptomatic Thrombocytopenia and Macrothrombocytosis in the Cavalier King Charles Spaniel

By Dr. Kim Hamer, DVM

  1. Platelets are also called thrombocytes. These are the blood cells that are responsible for normal blood clotting.
  2. Thrombocytopenia is an abnormally low blood platelet count.
  3. Macrothrombocytes are abnormally large blood platelets.

Normal blood platelet counts should be between 150-200,000. Dogs will have bleeding abnormalities if their counts are below 40,000. However, Cavaliers may have counts well below 40,000 with no problems.

Approximately 30% of Cavaliers have macrothrombocytosis and/or thrombocytopenia. This appears to be a congenital abnormality. The Cavalier does not experience any health problems despite these changes. It is thought that the large platelets of the Cavalier are able to provide the same function in lower numbers than that of other breeds.

Because Cavalier platelets are so large, automated cell counters may mistakenly count them as white blood cells, artificially lowering the platelet count. Additionally, these cells may not be recognized when examined under the microscope on a blood smear because they may not look like the platelets of other breeds.

This condition should not be confused with immune-mediated thrombocytopenia, where the body attacks its platelets. Dogs with this disorder will have SYMPTOMS: i.e. petechiae, bruising and bleeding.

Remember, the Cavalier does not experience any health problems due to this condition, which has only been reported in our breed and no others!

NOTE: This information was provided as a handout during the seminar presented to the Cavalier King Charles Spaniel Club of Greater Atlanta. Please feel free to share this information with your Veterinarian.