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Updated October 12, 2023 – Bloodwork is a routine part of a pet's healthcare journey, from yearly check-ups to pre-surgical screenings and diagnostic assessments. While many of us are familiar with blood tests, understanding the details of a comprehensive blood panel can be challenging. This article aims to demystify one of the most common tests on companion animals – the complete blood count.

What Does a CBC Measure?
The CBC provides a comprehensive tally of the various cells coursing through your pet's bloodstream: red blood cells (cells that carry oxygen from lungs to tissues), white blood cells (infection fighters), and platelets (clot-forming cells). Additionally, it offers crucial supplementary information to aid interpretation.

While most CBC is automated, technicians examine a blood sample under a microscope. This crucial step helps identify abnormal cells and parasites residing in red blood cells, providing invaluable insights for veterinarians.

Red Blood Cell Analysis

  • Red blood cell count: Reflects the number of cells circulating in the blood stream. A low count may indicate anemia, prompting further diagnostics. Conversely, a high count may signal dehydration or high-altitude living.
  • Hemoglobin: This protein carries oxygen and carbon dioxide within red blood cells. Levels vary depending on altitude. Low levels also indicate anemia. (Quick note here -- if you've ever had bloodwork done, spoken with your doctor or been hospitalized, you might've noticed that human docs tend to focus more on hemoglobin than other red cell parameters. Veterinarians tend to talk more about the hematocrit).  
  • Hematocrit: Reveals the proportion of blood volume occupied by red blood cells, offering another gauge of anemia and hydration.
  • Mean corpuscular volume: Indicates the size of red blood cells. Elevated MCV values may suggest faster cell turnover due to bleeding or specific types of anemia.
  • Mean corpuscular hemoglobin concentration: Calculates average hemoglobin concentration per red blood cell, aiding in identifying underlying anemia types. If anemia is identified, the MCHC can help determine what kind of anemia might be present (and yes, different types of anemia caused by other underlying problems).

What About White Blood Cells?
The differential count provides insight into the types and quantities of white blood cells (leukocytes). It offers percentages and absolute counts, indicating normal cell type ratios and any imbalances.

Specific Cell Types:

  • Neutrophils: Common infection-fighting cells, crucial for inflammation and infection responses.
  • Band cells: Immature neutrophils. Elevated counts may signal serious infections. Elevated numbers indicate that the bone marrow is increasing production because mature neutrophils are being consumed.
  • Eosinophils: Elevated during parasitic infections (heartworms), asthma and allergic reactions.
  • Basophils:  Associated with ectoparasitic infections (mites or lice), containing histamine involved in allergies. These are the rarest type of WBC.
  • Monocytes: Crucial immune cells that differentiate into macrophages (big eaters) and dendritic cells (cells with feet), responding to infection and disease. Monocytes are important cells of the immune system. Monocytes are elevated in many conditions including, stress, hormonal diseases and immune-mediated diseases.
  • Lymphocytes: Specialized white blood cells involved in antibody production and cell destruction, with implications for infection, cancer and immune compromise. Lymphocytes are much more specific in their actions than the cells discussed above but are also slower to respond. Low levels can indicate a disease process that is causing immune compromise. Lymphocyte counts also are lowered by steroid administration.

Finally, we have platelets.

  • Platelets are vital for blood clotting. Abnormal counts can signify immune-mediated diseases, blood loss, or usage. Sometimes, platelet clumps can artificially lower the platelet count. However, when a laboratory technician reviews the count under the microscope, they can see the clumps and note their findings in the final CBC report.

The amount of information gained from this relatively simple test is truly amazing! The CBC remains a cornerstone of diagnostic testing for all animal diseases, including species as diverse as reptiles, birds and other wildlife. If your pet has an abnormal result on their CBC, it's very important to discuss these findings with your veterinarian.

Did you know the Foundation was one of the first to support CBC use in wildlife?
One of the first wildlife studies ever funded by the Foundation, back in 1967, provided support for a survey of bloodwork for captive, conservation animals. It's hard to imagine that this routine test hadn't been applied much to species other than domestic animals. This important early study helped lay the groundwork for establishing normal CBC values for these neglected animals and identifying important parasites affecting certain populations.

This type of work is only possible through the support of our donors, who believe in advancing the health of all animals. From the most complex bench research study to clinical trials, our supporters have helped us fund more than 3,000 studies.

Learn more about how you can help us continue to improve the health and well-being of all animals!

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