White Blood Cells (WBC)

What it measures

White blood cells are the body's immune cells and include neutrophils, lymphocytes, and other types. A high or low total has many causes, and clinical interpretation guides suggest looking at which type is changing rather than the total alone; the differential count on your report does exactly that.

What a high value may mean

The three most common causes are stress (more steroid hormones in the body), excitement (driven by adrenaline, especially noticeable in cats), and inflammation. When a cat is stressed at the clinic, lymphocytes and neutrophils can rise temporarily, and kittens under six months naturally have higher lymphocytes. In inflammation or infection, it is mainly neutrophils that increase.

What a low value may mean

Possible causes include severe infection drawing large numbers of white cells into tissues; viral infections such as feline panleukopenia, feline leukemia virus (FeLV), and feline immunodeficiency virus (FIV); bone marrow problems; and some drugs (such as chemotherapy). Stress or steroids commonly lower lymphocytes.

Usually read together with

The differential count (neutrophils, lymphocytes, monocytes, eosinophils, and so on) and a blood smear review.

When to follow up

If white cells are clearly low, especially in an unvaccinated kitten that is also vomiting, has diarrhea, a fever, or very low energy, see the vet promptly. If the count is only mildly high and the cat's energy and appetite are normal, your vet may judge it to be stress-related and arrange a recheck if needed.

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