Diagnosis of canine primary polycythemia and management with hydroxyurea.

Severe polycythemia was found in 3 dogs with PCV 68% to 70%. Direct RBC mass determinations were increased in all dogs, confirming absolute polycythemia. Cause for secondary polycythemia was not found in any of the dogs; serum erythropoietin concentrations were undetectable, consistent with primary polycythemia. The polycythemia and associated clinical signs were controlled successfully for extended periods (mean, 16.6 months), using phlebotomy followed by oral administration of hydroxyurea in loading and in daily maintenance dosages.