Low eosinophils in cats, called eosinopenia, most commonly results from stress, steroid medications, or acute infection. In healthy cats, absolute eosinophil counts typically range from 0.1 to 2.2 × 10³ cells per microliter of blood. When the count drops below 0.1 × 10³/µL, or to zero, your vet may flag it on bloodwork.
The good news: eosinopenia on its own is rarely the primary problem. It’s a signal pointing toward something else going on in your cat’s body. Here’s what can drive those numbers down.
Stress and the Cortisol Response
The single most common reason for low eosinophils in cats is stress. When a cat is stressed, whether from illness, pain, a car ride to the vet, or even being hospitalized, the body releases cortisol and adrenaline. These hormones do two things that shrink the eosinophil count: they block the bone marrow from releasing new eosinophils into the bloodstream, and they cause circulating eosinophils to migrate out of the blood and into body tissues where they can’t be counted on a standard blood test.
Vets often see this as part of a “stress leukogram,” a pattern on bloodwork that also includes elevated neutrophils, low lymphocytes, and sometimes elevated monocytes. If your cat’s results show that combination, the eosinopenia is likely a byproduct of the stress response rather than a separate concern. It can happen even in cats that seem calm, since internal pain or subclinical illness triggers the same hormonal cascade.
Steroid Medications
Corticosteroids like prednisolone, dexamethasone, and methylprednisolone are widely prescribed in cats for allergies, inflammatory bowel disease, and asthma. These drugs mimic cortisol and produce the same eosinophil-lowering effect as the body’s own stress hormones. Eosinophil counts typically drop shortly after a cat begins steroid treatment, and they stay low for the duration of the dosing period.
The drop is reversible. Eosinophil counts generally recover within a few days after the medication is stopped. If your cat is on any form of steroid, including topical ear or skin preparations, that’s the likely explanation for low eosinophils on bloodwork. Even a single injection of a long-acting steroid can suppress eosinophils for weeks.
Acute Infection or Severe Inflammation
Active bacterial infections, sepsis, and severe inflammatory conditions pull eosinophils out of circulation. During an acute infection, the immune system prioritizes neutrophils and other first-responder cells, while eosinophils get sidelined. The bone marrow temporarily shifts its production priorities, and circulating eosinophils are drawn into inflamed tissues.
In critically ill animals and humans, persistent eosinopenia has been studied as a potential marker of disease severity. While it’s not as reliable as other markers for predicting outcomes, a very low eosinophil count in a sick cat can reinforce the picture that the body is fighting something serious. Conditions like pyometra (uterine infection), peritonitis, or widespread bacterial infection can all drive eosinophils to zero.
Cushing’s Disease
Hyperadrenocorticism, commonly called Cushing’s disease, causes the adrenal glands to overproduce cortisol on a chronic basis. It’s relatively rare in cats compared to dogs, but when it occurs, one of the bloodwork findings can be eosinopenia as part of the stress leukogram pattern. Cats with Cushing’s often also show increased thirst, frequent urination, a pot-bellied appearance, and fragile skin that tears easily. The eosinopenia in these cases is persistent rather than a one-time finding, because the excess cortisol production is ongoing.
Bone Marrow Suppression
Less commonly, low eosinophils can reflect a problem with the bone marrow itself. Feline leukemia virus (FeLV) is one of the more well-known causes of bone marrow suppression in cats, potentially reducing the production of multiple blood cell types, including eosinophils. Certain toxins, chemotherapy drugs, and other medications can have a similar effect. In these cases, you’d typically see other cell lines affected too, not just eosinophils. Low red blood cells, low platelets, or low overall white blood cells alongside eosinopenia would point your vet toward investigating bone marrow function more closely.
When Low Eosinophils Are Not a Concern
Normal eosinophil counts in cats can range all the way down to 0.1 × 10³/µL, and some reference ranges list zero as the lower bound. This means a cat can have a very low eosinophil reading and still fall within the normal range. Eosinophils make up a small fraction of total white blood cells to begin with, typically 0 to 9 percent. A single low reading in an otherwise healthy cat, with no other abnormalities on bloodwork, is generally not meaningful. Eosinophil counts fluctuate throughout the day and can be affected by something as simple as the stress of the blood draw itself.
Your vet is most likely to investigate further if the low eosinophil count appears alongside other abnormal values, if your cat is visibly unwell, or if the pattern persists across multiple blood tests. Isolated eosinopenia in a cat that’s eating, drinking, and behaving normally rarely requires additional workup on its own.
What Typically Happens Next
If your vet flagged low eosinophils, the next steps depend entirely on the bigger picture. For a cat already on steroids, no further investigation is usually needed. For a cat that was stressed at the clinic, your vet may recommend rechecking bloodwork when the cat is calmer or at a later date. For a sick cat with other abnormal findings, your vet will focus on identifying and treating the underlying condition, whether that’s an infection, an endocrine disorder, or something else. As the root cause resolves, eosinophil counts typically return to normal on their own.