Basophils in cats and dogs

What it shows

Basophils are made in the bone marrow and carry granules that contain histamine and heparin — substances involved in allergic and inflammatory reactions. Merck notes that basophils are rare in all common domestic animals, and that because of this there is no clear interpretation for basophilia on its own.

With so few cells, the count is easily affected by chance: a smear differential counts only 100 white cells, so one basophil more or less changes the result noticeably. Canine basophils often have few visible granules and can be hard to recognise; feline ones are packed with pale lavender granules. Analyzers and people do not always agree about such rare cells, which is why a surprising result is checked on the smear.

Higher than reference — what it may be a sign of

• Together with eosinophilia — the most typical picture. Merck groups basophilia with eosinophilia as a reason to think of allergic inflammation and parasites.
• Heartworm (dirofilariasis): Merck notes that eosinophilia and basophilia, alone or together, may occur in dirofilariasis, and that basophilia does occur in some dogs with heartworm disease.
• Respiratory disease, mast cell tumours and lymphoma — in one study cited by eClinPath, basophilia in dogs was linked with these conditions, and in cats with respiratory disease.
• Chronic myeloid disorders — rare: here basophilia can occur without eosinophilia.

Lower than reference

A low basophil count is not a finding. Most healthy animals have no basophils in circulation, the lower limit of the reference range is usually zero, and eClinPath states that basopenia is not a relevant finding. A result of 0 on the form is normal for most cats and dogs.

Look at together with

• Eosinophils — the first thing to look at: basophilia alone is hard to interpret, together with eosinophilia it points toward allergy or parasites.
• Total white cell count (WBC) — needed to turn the percentage into an absolute number.
• Blood smear review — confirms that the cells really are basophils.
• Heartworm test in dogs — when eosinophils and basophils are up, as the vet decides.

Units and conversion

The absolute count (BASO, Baso#) is reported as ×10⁹/L (×10^9/л on Russian forms). The percentage (BASO%) is the share of basophils among all white cells. Absolute count = percentage × total WBC ÷ 100. With such rare cells the absolute count is what the vet reads; a percentage of 1 with a normal total WBC is a very small number of cells. In the app each row keeps the unit printed on the form.

Reference range

The reference range is on your lab’s form. It usually starts at zero and differs between species and analyzers. Because basophils are so rare, a single slightly raised value means little; a repeated rise, especially together with eosinophilia, is a reason for the vet to look further. A series of tests says more than one result.

Cats and dogs

Sources

1. eClinPath (Cornell University) — Individual WBC
2. eClinPath (Cornell University) — Normal leukocytes
3. eClinPath (Cornell University) — Leukogram
4. Merck Veterinary Manual — Physiology of Leukocytes in Animals
5. Merck Veterinary Manual — Leukogram Abnormalities in Animals
6. Merck Veterinary Manual — Heartworm Disease in Dogs, Cats, and Ferrets
7. Merck Veterinary Manual — White Blood Cell Disorders of Dogs (dog owners)