ABSTRACT
Polycythemia is a condition which, by definition, indicates that the erythrocyte count is higher than normal. It is an uncommon finding in birds. The hematocrit, as would be expected, is concurrently elevated, and in birds polycythemia is generally defined as a Hct greater than 70% (Mitchell and Johns 2008). There are two main forms of polycythemia, i.e., relative and absolute. Relative polycythemia is caused by hemoconcentration as a result of dehydration and is essentially a reduction of the plasma volume. This is recognized in the laboratory setting by comparing the red cell count or hematocrit with the concentrations of protein or other constituents of the plasma whose normal limits are established. In this case both the erythrocyte level and that of plasma protein are comparably increased. On the other hand, absolute polycythemia is a significant increase in the number of erythrocytes in the absence of clinical evidence of dehydration or laboratory indication of hemoconcentration. In this instance the most common clinical causes of avian absolute polycythemia center on hypoxia with the increased erythrocyte count representing a physiologic response to increase the level of oxygenation of the tissues (Fudge 1997). This version of polycythemia is categorized as secondary. Primary polycythemia is an unregulated elevation of the erythrocyte count caused by a myeloproliferative disorder such as erythrocytic leukemia.
