White blood cell count (WBC) in cats and dogs
The white blood cell count (WBC) is the total number of leukocytes — the cells that fight infection and respond to inflammation — in a volume of blood. It is a headline number: a high or low total says that something has changed, but which cells changed, and why, is read from the differential in absolute numbers.
What it shows
White blood cells are not one type of cell but five: neutrophils, lymphocytes, monocytes, eosinophils and basophils. The analyzer counts all nucleated cells and reports their sum. Nucleated red blood cells (immature red cells that still have a nucleus) can be counted as white cells by mistake, so when a lab sees more than 5 of them per 100 white cells it corrects the total.
On its own the total says little: eClinPath notes that an increase is not meaningful in itself and has to be read by the cell type responsible. That is why vets read it together with the differential — the split of the total into the five types — and the blood smear.
Higher than reference — what it may be a sign of
- Excitement (physiologic leukocytosis): fear at the visit releases epinephrine (adrenaline). According to the Merck Veterinary Manual, the total can double within minutes, mostly from mature neutrophils; young animals and cats often show more lymphocytes too.
- Stress leukogram: the body’s own corticosteroids (cortisol) during illness, pain or prolonged stress, or corticosteroid medicines. Typical pattern: more mature neutrophils, fewer lymphocytes and eosinophils.
- Inflammation and infection: the hallmark is a left shift — immature (band) neutrophils in the blood. Closed infections, such as pyometra (infection of the uterus) in dogs, can push neutrophils very high.
- Blood cancers, less often: many lymphocytes can come from lymphoma or chronic lymphocytic leukemia.
- Artefact: some analyzers count platelet clumps as white cells — especially in cats.
Lower than reference
A low count (leukopenia) usually means fewer neutrophils, fewer lymphocytes, or both.
- Few neutrophils (neutropenia): overwhelming bacterial infection or sepsis, when neutrophils are used up faster than the marrow supplies them; viral infections; idiosyncratic reactions to some medicines; immune destruction.
- Few lymphocytes (lymphopenia): most often stress or corticosteroids — a mild leukopenia of this kind may simply be a stress leukogram.
- Bone marrow damage: when white cells, red cells and platelets all fall (pancytopenia), the vet thinks of toxins, some medicines, marrow tumours or ehrlichiosis. Neutrophils often drop first: they circulate for only about 10–15 hours.
A sample stored too long before the run can also give a falsely low count.
Look at together with
- Neutrophils, lymphocytes, monocytes and eosinophils in absolute numbers — they explain what moved the total.
- Blood smear — band neutrophils, toxic change in neutrophils, platelet clumps, abnormal cells.
- Platelets and hemoglobin — when all three cell lines are low, the question moves to the bone marrow.
Units and conversion
The count is reported as 10⁹/L (the SI unit) or as thousands per microlitre — 10³/µL, K/µL, or тыс/мкл on Russian-language forms. The factor is 1: 12 × 10⁹/L equals 12 × 10³/µL.
The differential is often printed twice: as a share in % and as an absolute count in the same units as WBC. Vets read the absolute numbers. eClinPath’s example: 30% eosinophils with a low-normal total may be no increase at all, while 30% of 20 × 10⁹/L is 6 × 10⁹/L — a clear excess. In the app each row keeps the unit from the form, and the chart converts everything to one unit.
Reference range
The reference range is on your lab’s form. It depends on species, age and analyzer. A reference interval is built so that a small share of healthy animals — about 2.5% — sit above its upper limit. A mildly high count in a calm, healthy-looking animal, or in a cat that was frightened at the visit, often reflects excitement or stress rather than disease. The differential, the smear and a repeat count say more than one total.
Cats and dogs
In cats the excitement response is especially marked: according to the Merck Veterinary Manual, lymphocytes in an excited cat can reach about twice the upper reference value, and young cats show it most. Cats are also the species in which platelet clumps most often inflate the white cell count on some analyzers. Among the causes of a low count, panleukopenia and FeLV are typical for cats.
In dogs the stress leukogram usually includes more monocytes as well as fewer lymphocytes and eosinophils. Closed infections, such as pyometra, can raise neutrophils to around 100 × 10⁹/L. Among viral causes of a low count, the Merck Veterinary Manual names parvovirus and the acute phase of distemper for dogs.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.