Most anemias can be classified using the reticulocyte count, PCV, MCV, and MCHC. Regenerative anemias are characterized by reticulocytosis. Polychromasia and increased MCV usually are present. Hemolytic mechanisms and hemorrhage should be considered in a systemic evaluation of the blood and the patient. In animals with chronic external blood loss, a microcytic, hypochromic anemia develops secondary to iron deficiency. Nonregenerative anemias generally are characterized by normocytic, normochromic erythrocytes and the lack of reticulocytosis. Patients with nonregenerative anemia should be evaluated for chronic inflammation or neoplasia, renal disease, endocrine insufficiency, or hypoplasia of the bone marrow.