Toxic change in neutrophils on a blood smear in cats and dogs
Toxic change is a description of how neutrophils look on a stained blood smear, not a count from the analyser. It shows that the bone marrow is producing neutrophils in a hurry, cutting their maturation short — usually because of strong inflammation somewhere in the body. Despite the name it does not mean poisoning, and it is a clue for the vet, not a diagnosis.
What it shows
When inflammation drives the marrow hard, neutrophils are released before they have fully matured. They keep features of young cells, which the person reading the smear recognises as:
- Cytoplasmic basophilia — streaky, bluish cytoplasm.
- Döhle bodies — small pale blue patches in the cytoplasm; often the earliest sign.
- Foamy vacuolation — an indistinct, bubbly look of the cytoplasm.
- Immature nucleus — lighter, finer chromatin; the subtlest feature.
- Toxic granulation — distinct red granules; rare in cats and dogs, seen more often in horses and ruminants.
The name comes from early observations in people with severe bacterial blood infection; in animals it is linked with inflammation in general rather than with toxins.
Higher than reference — what it may be a sign of
- Strong inflammation. Toxic change is most marked with sepsis, endotoxaemia and tissue necrosis. Examples described in cats include bacterial infections (pneumonia, peritonitis, septicaemia), viral infections (parvovirus, upper respiratory viruses) and metabolic disorders such as ketoacidotic diabetes and hepatic lipidosis.
- Recovery of the marrow after injury, or medicines that stimulate neutrophil production.
Toxic change often comes with a left shift — band and younger neutrophils in blood — but in rare cases appears without one, and the neutrophil count itself may be low, normal or high. When toxic change appears without a left shift, the lab also considers a storage artefact or a marrow disorder.
Lower than reference
“Not seen” is the usual result in a healthy animal, but it does not rule out inflammation. Some animals have a left shift without toxic change. Stored blood works the other way: in EDTA blood kept at room temperature, Döhle-like bodies appeared in 1 of 8 samples after 4 hours and in all 8 after 24 hours, and vacuoles also appear early. Cooling slows this, which is why a smear made at collection is sent with the tube.
Look at together with
- Neutrophils — the absolute count and the bands (left shift).
- Manual differential — toxic change is described from the same smear.
- Total white cell count — the overall picture of the leukogram.
- C-reactive protein in dogs and serum amyloid A in cats — other markers of inflammation.
Units and conversion
There are no units: this is a description of cells on the smear. Some labs grade it in words — mild, moderate or marked — others with a scale from 1+ to 3+ or 4+. Grading is subjective and can differ between labs, so it is most useful when the same lab follows one animal over time. In the app the result is stored as text, as written on the form.
Reference range
The reference range is on your lab’s form. There is no number to compare against: the lab notes whether toxic change is present and how marked it is. In healthy dogs it is not expected; in healthy cats a few small Döhle bodies may be the only finding.
Cats and dogs
Unlike other species, apparently healthy cats can have a few small Döhle bodies, so on their own they are counted as only mild toxicity. Red toxic granulation is rare in cats, and the reddish granules seen in healthy Birman, Siamese and Himalayan cats are a normal breed feature, not toxic change.
In dogs toxic change usually goes with an inflammatory leukogram and often with a left shift.
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
- eClinPath (Cornell University College of Veterinary Medicine). Toxic change.
- eClinPath (Cornell University College of Veterinary Medicine). Smear examination.
- Today’s Veterinary Practice. Blood Smear Review: How to Identify and Interpret Neutrophil Abnormalities.
- Harvey JW. The feline blood film: 2. Leukocyte and platelet morphology. Journal of Feline Medicine and Surgery, 2017.
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.