ALTERED PLATELET INDEXES IN DOGS WITH HYPOTHYROIDISM AND CATS WITH HYPERTHYROIDISM

Changes in platelet indices (platelet count and platelet size) and PCV associated with thyroid disease were studied in 7 dogs with hypothyro idism and 21 cats with hyperthyroidism that were admitted to the veter inary teaching hospital. Compared with control (euthyroid) dogs, dogs with hypothyroidism had higher platelet count (P = 0.003), smaller pla telet size (P = 0.01), and lower PCV (P = 0.02). Comparison of the gro up of hyperthyroid cats with a group of similarly aged, clinically nor mal cats with normal thyroxine values indicated that the group of hype rthyroid cats had significantly (P = 0.03) higher mean platelet size t han did control cats, but differences were not found in mean platelet count or PCV. Results of this investigation indicate that the changes in platelet size reported in human beings with thyroid endocrinopathie s also are found in animals so-affected. Although the pathogenesis of platelet abnormalities in animals with thyroid derangement is unclear and likely is multifactorial, the observed relation between platelet a nd erythrocyte production in this group of dogs is consistent with rep orts of an inverse relation between thrombocytopoiesis and erythropoie sis in iatrogenically hyperthyroid mice and in mice exposed to hypoxia .