Appropriate secondary absolute erythrocytosis in a horse.

This research examines the occurrence of a rare form of increase in red blood cell count, known as secondary absolute erythrocytosis, in a horse. This paper discusses the causes, effects, and link to certain health conditions.

Understanding Erythrocytosis

• Erythrocytosis is a condition characterized by an increase in red blood cell (RBC) count. This could be caused by conditions like dehydration or splenic contraction, leading to relative erythrocytosis, which is more common.
• However, there’s also absolute erythrocytosis where there is an actual increase in the number of RBCs. This type can be primary or secondary and is quite rare in horses.
• Primary erythrocytosis is characterized by an increase in cells of the erythroid lineage (related to RBC production) without an increase in erythropoietin, a hormone that controls red blood cell production.

Understanding Secondary Erythrocytosis

• Secondary erythrocytosis involves an increase in erythropoietin level. It can be appropriate or inappropriate.
• Appropriate secondary erythrocytosis is usually a response to tissue hypoxemia (insufficient oxygen in the tissues), which could be due to various factors like congenital heart disease, severe chronic pulmonary or cardiovascular diseases, high altitude or changes in haemoglobin.
• On the other hand, inappropriate erythrocytosis involves the release of erythropoietin or substances similar to it in response to renal hypoxia (lack of oxygen supply to the kidneys) or neoplasia, a condition characterized by abnormal growth of cells.

Potential Risks and Symptoms

• If the haematocrit (the volume percentage of red blood cells in blood) rises above 60%, the benefits of greater oxygen transport could be nullified by the detrimental effects of increased blood viscosity (thickness).
• In horses, symptoms of erythrocytosis can include lethargy, weight loss, dark-coloured blood, deep red to purple mucous membranes, normal to slightly increased capillary refill time, high heart and breathing rates, mild cyanosis (bluish discoloration of the skin), haemorrhagic episodes (bleeding), and thrombosis (clotting).
• Absolute erythrocytosis in large animals is typically caused by congenital cardiac anomalies.
• Erythrocytosis that is secondary to congestive cardiac failure or chronic pulmonary disease is uncommon in all species and is usually mild.