Blood cells circulate through the body in the blood vessels. This makes it vital that the number of cells be maintained at appropriate levels. When cell numbers are outside the normal range, they can indicate a health problem. The complete blood count involves counting cell numbers and, for some cells, measuring their size and determining substances like hemoglobin. Cells that are counted include the red blood cell (RBC or erythrocytes), white blood cells (WBC or leukocytes) and platelets (thrombocytes). The end of the names (-cytes) means cells.

Each cell type responds in characteristic ways to illness. This means information from their evaluation can be used to aid the process of making a diagnosis, determining the need for additional testing and monitoring the response to therapy. For example, a dog that has an increased WBC count may have a bacterial infection (not the only possible reason). Along with physical exam findings, response to antibiotic therapy could be monitored by periodically repeating the WBC counts during therapy.

The RBC is involved with transport of oxygen and carbon dioxide. When RBCs get too low (anemia), not enough oxygen can be transported. RBCs have to be replaced regularly. They are made in the bone marrow of adults and released into the circulation when signaled by a substance produced mainly by the kidney. Development of RBCs in the bone marrow requires certain nutrients like B vitamins, n3 fatty acids (lipids for the cell membrane) and iron (for hemoglobin).

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Sometimes the bone marrow releases RBCs before they are fully mature. Reticulocytes are RBCs that are one step from being mature RBCs. They are released from the bone marrow to replace the aging RBCs, so low levels are normal. However, in response to anemia, the number of reticulocytes in the blood should increase. A lack of increase shows that the body is not responding to the anemia. This would suggest the need for additional investigation to identify the cause of anemia. Interestingly, measurement of reticulocyte hemoglobin levels has shown value for recognizing the presence of inflammatory conditions in the body.

The WBC is another important cell type group in blood. They function as part of the immune system and play an important role in defense of the body. WBC is a general term that refers to a group of cells that include the neutrophil, monocyte, lymphocyte, eosinophil and basophil. Each has a unique function and is found in characteristic amounts in the blood normally.

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The numbers of each type and the overall WBC count provide information about a range of body conditions. Comparing numbers to normal levels and the overall pattern of numbers is valuable. In our example above, an increased neutrophil count was associated with an infection. This could be supported by seeing an increased monocyte count. The monocyte arrives a few days after an infection to aid in the “clean up.” However, sometimes there can be a temporary neutrophil increase from stress not associated with infection. This would be seen as an increased neutrophil number and a reduced lymphocyte number. It is clear that these patterns of cell numbers can be informative but not always definitive.

Lymphocytes are important cells in the immune response. They respond to viral infections and produce antibodies. Eosinophils and basophils are part of the response to allergies, but they also function as part of the immune response.

Platelets are part of the blood clotting process.

This brief overview gives a glimpse of why the complete blood count is an important part of assessing health and making a diagnosis. There is so much more to the story. Contact your veterinarian if you have questions about the complete blood count.

Ron Carsten, DVM, PhD, CVA, CCRT was one of the first veterinarians in Colorado to use the integrative approach, has lectured widely to veterinarians, and has been a pioneer in the therapeutic use of food concentrates to manage clinical problems. He is also the founder of Colorado Animal Rescue (CARE). In addition to his Doctor of Veterinary Medicine, he holds a PhD in Cell and Molecular Biology and is a Certified Veterinary Acupuncturist and Certified Canine Rehabilitation Therapist. He practices integrative veterinary medicine in Glenwood Springs.