The most important causes of erythrocytosis in cats and dogs

10/03/2025

1. Primary absolute erythrocytosis: Occurs when there is increased RBC proliferation in the absence of erythropoietin. It is a manifestation of neoplastic myeloproliferative diseases, especially polycythemia vera.

2. Secondary Absolute Erythrocytosis: It is caused by increased erythropoietin concentrations that stimulate erythroid hyperplasia in the bone marrow, increasing RBC production, and may be associated with endocrinopathy.

The clinical manifestations of erythrocytosis are due to hyperviscosity caused by increased RBC mass, and the symptoms may vary depending on the degree and duration of the increase in hematocrit. Symptoms may include changes in mucosal color (erythematous or cyanotic mucosa), increased capillary refill time (CRT), tachycardia, neurological disorders due to hypoxic damage, pain, thrombosis, and hemorrhage.

When the causes of erythrocytosis are listed, the following are highlighted:

1. Dehydration and splenic contraction (Relative erythrocytosis): Dehydration can artificially increase hematocrit due to decreased body fluids. Erythrocytosis due to dehydration can be treated with fluids to correct the volume deficit. The type and route of fluid administration should be determined by the degree of dehydration, the underlying condition causing the dehydration, and other metabolic abnormalities. Splenic contraction triggers the release of blood stored in the spleen into the circulation, which is mediated by the release of epinephrine.

2. Hypoxemia (Secondary appropriate absolute erythrocytosis): Tissue hypoxia due to chronic hypoxemia may increase erythropoietin secretion and lead to appropriate absolute erythrocytosis.

3. Erythropoietin-secreting neoplasms (Secondary inappropriate absolute erythrocytosis): Tumors may increase erythrocyte production, leading to inappropriate absolute erythrocytosis. This is an inappropriate response because erythropoietin production increases in the absence of systemic hypoxia. These tumors are most often of renal origin, but other tissue tumors (nasal fibrosarcoma, hepatocellular carcinoma, schwannoma, and cecal leiomyosarcoma) may also secrete erythropoietin. Renal tumors should be confirmed because other renal lesions, including pyelonephritis, can also lead to inappropriate secondary erythrocytosis. Treatment includes removal of the erythropoietin-secreting neoplasm and management of erythrocytosis using therapeutic phlebotomy and fluid support with IV crystalloids.

4. Erythrocytosis due to endocrinopathy (Secondary absolute erythrocytosis): Hormones can directly or indirectly stimulate erythropoiesis. However, erythrocytosis due to endocrinopathy is usually mild and insufficient to cause clinical symptoms.

5. Myeloproliferative neoplasia (Polycythemia vera: Primary absolute erythrocytosis): Polycythemia vera is a chronic myeloproliferative disorder characterized by increased blood volume. The pathogenesis involves the rapid production of increased numbers of erythrocytes with a normal to prolonged half-life in the blood. Treatment includes therapeutic phlebotomy and myelosuppressants to reduce blood viscosity and normalize hematocrit. Appropriate treatment methods and follow-up processes may vary depending on the cause of erythrocytosis. Therefore, correct diagnosis and treatment are important in the management of patients with erythrocytosis.