Congenital Macrothrombocytopenia (Cairn and Norfolk Terrier Type) is an inherited blood condition affecting dogs. This condition is diagnosed via microscopic examination of a blood smear. It is characterized by reduced numbers of normal sized Platelets in the blood (thrombocytopenia) and the presence of large platelets (macrothrombocytes). Affected dogs rarely exhibit clinical signs related to platelet abnormalities however, recognizing a congenital cause for macrothrombocytopenia is important because both the lack of platelets and large platelets can be associated with other clinically important diseases. In addition, some blood analyzer machines can misinterpret macrothrombocytes as red blood cells, thus further complicating diagnoses. Dogs affected with this condition do not show increased incidence of Hemorrhage and blood clotting times are normal.