Interpreting the Complete Blood Count

Comprehensive Guide to Interpreting the Complete Blood Count (CBC) in Canine and Feline Patients

A Complete Blood Count (CBC) is an essential diagnostic tool in veterinary medicine, providing critical insights into the hematologic status of canine and feline patients. This guide offers an in-depth analysis of each CBC component, elucidating their clinical significance, interpretation, and associated pathologies.

Red Blood Cell (RBC) Parameters

1. Hematocrit (HCT) / Packed Cell Volume (PCV)

• Definition: HCT is the calculated percentage of blood volume occupied by RBCs, while PCV is the directly measured value obtained via centrifugation.

• Interpretation:

  • Increased: Dehydration, splenic contraction, polycythemia vera, hypoxia-induced erythrocytosis.

  • Decreased: Anemia due to hemorrhage, hemolysis, or decreased production.(eclinpath.com)

2. Red Blood Cell Count (RBC)

• Definition: The total number of RBCs per unit volume of blood.

• Interpretation:

  • Increased: Absolute polycythemia, relative polycythemia due to dehydration.

  • Decreased: Anemia of various etiologies.

3. Hemoglobin (HGB)

• Definition: The concentration of hemoglobin within the blood.

• Interpretation:

  • Increased: Polycythemia, dehydration.

  • Decreased: Anemia, hemodilution.(eclinpath.com)

4. Mean Corpuscular Volume (MCV)

• Definition: The average volume of individual RBCs.

• Interpretation:

  • Increased (Macrocytosis): Regenerative anemia, FeLV infection, myelodysplasia.

  • Decreased (Microcytosis): Iron deficiency anemia, portosystemic shunts.

5. Mean Corpuscular Hemoglobin (MCH)

• Definition: The average amount of hemoglobin per RBC.

• Interpretation:

  • Increased: Spherocytosis, hemolysis.

  • Decreased: Iron deficiency anemia.

6. Mean Corpuscular Hemoglobin Concentration (MCHC)

• Definition: The average concentration of hemoglobin in RBCs.

• Interpretation:

  • Increased: Hemolysis, spherocytosis.

  • Decreased: Iron deficiency anemia, regenerative anemia.

7. Red Cell Distribution Width (RDW)

• Definition: A measure of the variation in RBC size (anisocytosis).

• Interpretation:

  • Increased: Regenerative anemia, iron deficiency anemia.

  • Decreased: Not clinically significant.

8. Reticulocyte Count

• Definition: The number of immature RBCs, indicating bone marrow response.

• Interpretation:

  • Increased: Regenerative anemia.

  • Decreased: Non-regenerative anemia.

9. Nucleated Red Blood Cells (nRBCs)

• Definition: Immature RBCs with nuclei present in peripheral blood.

• Interpretation:

  • Increased: Regenerative anemia, bone marrow damage, splenic dysfunction.

White Blood Cell (WBC) Parameters

1. Total WBC Count

• Definition: The total number of WBCs per unit volume of blood.

• Interpretation:

  • Leukocytosis: Infection, inflammation, stress, leukemia.

  • Leukopenia: Bone marrow suppression, viral infections.

2. Differential WBC Count

• Neutrophils:

  • Neutrophilia: Infection, inflammation, stress response.

  • Neutropenia: Severe infection, bone marrow suppression.

• Lymphocytes:

  • Lymphocytosis: Chronic infection, lymphoid leukemia.

  • Lymphopenia: Stress, corticosteroid therapy.

• Monocytes:

  • Monocytosis: Chronic inflammation, stress response.

  • Monocytopenia: Not typically significant.

• Eosinophils:

  • Eosinophilia: Parasitic infections, allergies.

  • Eosinopenia: Stress response.

• Basophils:

  • Basophilia: Parasitic infections, hypersensitivity reactions.

  • Basopenia: Not typically significant.(eclinpath.com, sciencedirect.com)

Platelet Parameters

1. Platelet Count

• Definition: The number of platelets per unit volume of blood.

• Interpretation:

  • Thrombocytosis: Inflammation, neoplasia.

  • Thrombocytopenia: Immune-mediated destruction, DIC, bone marrow suppression.

2. Mean Platelet Volume (MPV)

• Definition: The average size of platelets.

• Interpretation:

  • Increased: Regenerative response to thrombocytopenia.

  • Decreased: Bone marrow suppression.

Blood Smear Examination

A manual review of a blood smear is crucial for identifying morphological abnormalities that automated analyzers may miss. This includes evaluation of RBC morphology (e.g., spherocytes, schistocytes), WBC morphology (e.g., toxic changes, left shifts), and platelet estimation. (vin.com, eclinpath.com)

Common Hematologic Patterns and Their Clinical Significance:

1. Regenerative Anemia

• Findings: Anemia with increased reticulocytes, polychromasia, anisocytosis.

• Causes: Hemorrhage, hemolysis.

2. Non-Regenerative Anemia

• Findings: Anemia with normal or decreased reticulocyte count.

• Causes: Chronic disease, bone marrow disorders.

3. Stress Leukogram

• Findings: Neutrophilia, lymphopenia, monocytosis, eosinopenia.

• Causes: Endogenous or exogenous corticosteroids.

4. Inflammatory Leukogram

• Findings: Neutrophilia with left shift, monocytosis, possible toxic changes.

• Causes: Infection, inflammation.

Reference Intervals

Note: Reference intervals may vary based on laboratory standards and should be interpreted in the context of individual patient factors.

Conclusion:

Interpreting a CBC requires a comprehensive understanding of each parameter and its clinical implications. Integrating CBC results with clinical findings and other diagnostic tests is essential for accurate diagnosis and effective patient management.

References:

1. EClinPath: Hematology. Cornell University College of Veterinary Medicine. https://eclinpath.com/hematology/

2. EClinPath: Hematology Tests. Cornell University College of Veterinary Medicine. https://eclinpath.com/hematology/tests/

3. EClinPath: Blood Smear Examination. Cornell University College of Veterinary Medicine. [https://eclinpath.com/hematology/hemogram-basics/blood-smear-examination/](https://eclinpath.com/hemat