Overview

Pet Education has information about the complete blood count and what it means.

White Blood Cells (CBC): Infection or Inflammation                                        Back to Page Index

White blood cells, sometimes called leukocytes, are the body's defence system. If inflammation or infection are present anywhere in the body, white blood cells will accumulate there to fight the invaders, and therefore the total number of white blood cells will increase. Albumin levels may also be elevated.

There can be other causes of increased white blood cells, such as the use of corticosteroids. WBCs are often very high in cases of acute renal failure. Cats with very high WBC levels may have increased potassium levels.

In contrast, cats on methimazole for hyperthyroidism may have low white blood cells.

There are four main types of white blood cells, divided into two groups:

Granulocytes:

• Neutrophils

• Eosinophils

Agranuloctyes:

• Lymphocytes

• Monocytes

There are also basophils but these are only rarely seen.

In order to work out where the problem lies, it is necessary to differentiate between how many of each type of WBC there are. This is called the differential count, and it usually shows two sets of numbers: the actual amount of each type of WBC (abbreviated as absolute or ABS); and the percentage of each type.

Pet Place has some information about WBCs (no need to register to read the article, just click on Close at the bottom of the irritating pop-up).

Pro Vet explains more about the differential count.

RnCeus has a good overview of WBCs.

Cornell University College of Veterinary Medicine explains more about WBCs.

Neutrophils

Neutrophils are the most numerous white blood cell. They are produced in the bone marrow. High neutrophils usually indicate the body is fighting a bacterial infection, though sometimes levels are high because of stress or inflammation.

Mature neutrophils are called segs (segmented cells) whilst immature ones are called bands. If a bacterial infection is present, more bands are released into the blood than would normally be the case to help fight it, so the percentage of bands increases compared to segs (sometimes called "a shift to the left"). The higher the number of bands, the more severe the infection.

In contrast, neutrophils are often low in cases of viral infection. They may also be low in cases of severe inflammation or bacterial infection where the body has struggled to keep up with the demand for them. Cats lacking Vitamin B12 and/or folic acid may have low neutrophil levels.

There is also something called a stress leukogram, which occurs when a cat has a chronic illness. In such a case the cat may have a high neutrophil count (an increase in segs rather than bands) with a low lymphocyte count.

Bio Chem Web has a great video of a neutrophil hunting a bacterium.

Cornell University College of Veterinary Medicine has some information about segs.

Cornell University College of Veterinary Medicine also has some information about bands.

Eosinophils

Eosinophils are also produced in the bone marrow. Levels are often high because of acute or chronic inflammation e.g. that caused by IBD, asthma or allergies. Other possible causes include parasites and occasionally lymphoma, a type of cancer.

Cats on steroids may have low eosinophil levels. Cats with acute or chronic inflammation or infection may also have low eosinophil levels.

Cornell University College of Veterinary Medicine has some information about eosinophils.

Lymphocytes

As the name suggests, lymphocytes are produced by the lymph glands, and also by the spleen. They consist of B cells and T cells. B cells work by producing antibodies which neutralise the threat, T cells work with other cells to do the same thing.

Lymphocytes are often low in cases of viral infection or when using steroids. They may also be low in cases of chronic bacterial infections. CKD cats with uraemia (which tends to apply to most CKD cats) often have low lymphocytes, as may cats on steroids. Lymphocytes may be increased in cases of chronic infection or inflammation, autoimmune disease or leukaemia (cancer of the blood). Cats taking medications for hyperthyroidism may also have elevated lymphocyte levels.

Cornell University College of Veterinary Medicine has some information about lymphocytes.

Monocytes

Monocytes can be produced in either the bone marrow or the spleen. They are capable of leaving the blood stream to enter surrounding tissues in order to reach hostile bacteria. They also remove damaged body cells, so are often present when there is tissue necrosis (dying tissue). Their numbers do not usually vary much unless leukaemia (cancer of the blood) is present.

Cornell University College of Veterinary Medicine has some information about monocytes.