Anemia, Polycythemia, and Blood Metabolism

A healthy regenerative response is identified by an increase in reticulocytes—immature red blood cells—in the peripheral blood. In extreme or severe cases of anemia, the bone marrow may release even more immature nucleated red blood cells (NRBCs) into the circulation.

Exam Tip: Species Exceptions While reticulocytes are the standard marker for regeneration in most domestic animals, horses are an exception. Horses do not release reticulocytes during anemia; therefore, a bone marrow aspirate or biopsy is required to confirm regeneration in these patients.

Polycythemia: Erythrocytosis and Erythrocythemia

Conversely, polycythemia (also referred to as erythrocytosis or erythrocythemia) involves an increased PCV, indicating a higher-than-normal proportion of red blood cells. This is categorized into two main types:

1. Relative Polycythemia

This is not a true increase in the total mass of red blood cells, but rather a perceived increase due to a decrease in plasma volume. The most common cause is dehydration (e.g., from vomiting or diarrhea). In cases of dehydration, both the PCV and total protein will typically increase.

2. Absolute Polycythemia

This involves a true increase in RBC production and is subdivided into:

• Appropriate (Compensatory) Polycythemia: The body produces more RBCs to compensate for hypoxia, such as in animals living at high altitudes or those with congestive heart failure.
• Inappropriate Polycythemia: The body produces excess RBCs without a physiological need for more oxygen transport. This can be caused by EPO-secreting tumors or polycythemia vera, a rare bone marrow cancer where the marrow autonomously overproduces abnormal, immature erythroid cells.

Blood Metabolism and Jaundice

Proper handling of blood samples is vital for accurate diagnostics. Because RBCs are living cells, they continue to consume glucose for energy even after being collected. If a sample is not centrifuged promptly to separate the cells from the plasma, the glucose levels may drop artificially, potentially leading to a misdiagnosis of conditions like diabetes mellitus.

When RBC destruction is excessive, it leads to hyperbilirubinemia (excess bilirubin in the blood), which manifests clinically as jaundice (icterus)—a yellow discoloration of the mucous membranes and the sclera. This is classified by the location of the pathology:

• Prehepatic Hyperbilirubinemia: Caused by excessive hemolysis (RBC breakdown) that produces more unconjugated bilirubin than the liver can process.
• Hepatic Hyperbilirubinemia: Caused by liver disease, where the liver is unable to effectively conjugate the bilirubin.
• Posthepatic Hyperbilirubinemia: Caused by a bile duct obstruction, preventing conjugated bilirubin from being excreted into the intestines.

Venipuncture and Hemostasis

During venipuncture, the insertion of a needle creates a small hole in the blood vessel wall. To prevent bleeding, the body relies on platelets (thrombocytes) to adhere to the injury site and undergo aggregation, forming a platelet plug.

Clinical Tip: Post-Venipuncture Care After removing the needle, apply gentle pressure to the site to assist the formation of the platelet plug. Avoid rubbing or repeatedly wiping the area, as this can disrupt the developing plug and prolong bleeding.

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Summary Table: Blood Component Abnormalities