Anemia in cats happens when red blood cell levels drop below the normal range, which sits between 31% and 48% on a standard blood test. The causes range from something as simple as a flea infestation to serious conditions like kidney disease or cancer. Understanding the underlying cause matters because it determines whether a cat’s body can recover on its own or needs targeted treatment.
Broadly, feline anemia falls into two categories: regenerative, where the bone marrow ramps up production of new red blood cells to compensate, and non-regenerative, where the bone marrow can’t keep up. Each type points to a different set of causes.
Blood Loss From Parasites and Injury
Flea and tick infestations are one of the most common causes of anemia in cats, particularly in kittens. Each flea takes a tiny amount of blood, but a heavy infestation can drain enough over days or weeks to cause a significant drop in red blood cells. This is especially dangerous for small, young, or already weakened cats who have less blood volume to spare.
Hookworms are another major culprit. These intestinal parasites latch onto the gut lining and feed on blood, causing slow, steady loss that may not be obvious from the outside. Bleeding can also come from stomach or intestinal ulcers, internal inflammation, or trauma like a wound or injury. In all of these cases, the bone marrow typically responds by pushing out new red blood cells, making this a regenerative form of anemia, one that can resolve once the source of bleeding is controlled.
Infections That Destroy Red Blood Cells
Several infectious organisms directly attack and destroy a cat’s red blood cells. A blood parasite called Mycoplasma haemofelis is one of the most well-known. It attaches to the surface of red blood cells, damaging them and triggering the immune system to clear them from circulation faster than the bone marrow can replace them.
Feline leukemia virus (FeLV) causes anemia through multiple pathways. One subtype of the virus specifically shuts down red blood cell production in the bone marrow by infecting the stem cells responsible for making new blood cells. FeLV also suppresses the immune system, which leaves cats more vulnerable to secondary infections like Mycoplasma that cause further red blood cell destruction. The anemia from FeLV can be either regenerative or non-regenerative depending on how the virus is affecting the body.
Toxins and Household Dangers
Cat hemoglobin is unusually vulnerable to oxidative damage compared to other species, and the feline spleen is less efficient at filtering out damaged cells. This makes cats especially sensitive to a list of toxins that might seem harmless.
Acetaminophen (Tylenol) is one of the most dangerous. Owners sometimes give it to cats that appear to be in pain, not realizing that cats lack the liver enzymes to process it safely. Even a single dose can cause severe red blood cell damage. Onions are another serious threat. Cats fed homemade diets or meat-based baby food containing onion powder can develop enough damaged red blood cells to become seriously anemic. Research has shown that some baby foods contain enough onion powder to damage up to 50% of a cat’s red blood cells.
Other substances that cause this type of oxidative damage include zinc, copper, and propylene glycol, a preservative that was once used in semi-moist cat foods. The FDA banned propylene glycol from cat food in 1994 after studies linked it to red blood cell damage.
Chronic Kidney Disease
Kidney disease is one of the most common causes of non-regenerative anemia in cats, especially older ones. Healthy kidneys produce a hormone called erythropoietin, which signals the bone marrow to make new red blood cells. As kidney tissue deteriorates, erythropoietin production drops, and the bone marrow gradually slows its output. Red blood cells have a natural lifespan, so when old cells die off and aren’t replaced at the same rate, the total count steadily declines.
This type of anemia develops slowly, often over months, which means cats may adapt to lower red blood cell levels before showing obvious signs. The FDA has conditionally approved the first drug specifically for treating this form of anemia in cats, which works by stimulating red blood cell production even when the kidneys can no longer do so effectively.
Immune-Mediated Red Blood Cell Destruction
In immune-mediated hemolytic anemia (IMHA), a cat’s immune system mistakenly identifies its own red blood cells as foreign invaders and destroys them. In cats, this condition is usually secondary to an underlying trigger rather than occurring on its own. Common triggers include reactions to medications, cancers, and infections like FeLV or feline infectious peritonitis (FIP).
IMHA can cause red blood cell counts to plummet rapidly, making it one of the more urgent forms of anemia. Treatment focuses on suppressing the overactive immune response while addressing whatever triggered it in the first place.
Bone Marrow Problems and Chronic Disease
When the bone marrow itself is compromised, it simply cannot produce enough red blood cells to keep up with normal turnover. Cancer cells can infiltrate the marrow and crowd out the stem cells that produce blood. Immune-mediated diseases and chronic inflammation within the marrow have the same effect.
Even when the bone marrow is structurally intact, chronic inflammation anywhere in the body can impair its function. This is called anemia of chronic disease, and it shows up alongside many long-term illnesses in cats, including cancers and chronic infections. The inflammatory signals circulating in the bloodstream interfere with the bone marrow’s ability to efficiently produce and release red blood cells.
Genetic Causes
Some cats inherit a condition called pyruvate kinase deficiency, where red blood cells lack a key enzyme needed for energy production. Without it, red blood cells become unstable and break down prematurely, leading to chronic anemia. A survey by the UC Davis Veterinary Genetics Laboratory found the responsible mutation at significant frequency in Abyssinians, Bengals, Domestic Shorthairs and Longhairs, Egyptian Maus, Maine Coons, Norwegian Forest Cats, Siberians, Singapuras, and Somalis, among others. Genetic screening is recommended for these breeds, especially before breeding.
Signs to Watch For
Because red blood cells carry oxygen throughout the body, anemia affects nearly every system. The most visible sign is pale gums. Lift your cat’s lip and look at the tissue above the teeth: healthy gums are pink, while anemic gums appear white or very pale. Cats with anemia also tend to become lethargic, sleep more than usual, lose interest in food, and may breathe faster as the body tries to compensate for reduced oxygen delivery. Some anemic cats develop pica, an unusual behavior where they eat non-food items like cat litter.
Because anemia develops gradually in many cases, cats can appear relatively normal until their red blood cell count drops quite low. A sudden onset, such as from toxin exposure or acute blood loss, tends to produce more dramatic symptoms including collapse and rapid heart rate.
How the Cause Is Identified
A vet’s first step is a complete blood count, which reveals not just how low the red blood cells are but whether the bone marrow is responding. A high count of immature red blood cells (reticulocytes) indicates regenerative anemia, pointing toward blood loss, toxin exposure, or red blood cell destruction. A low reticulocyte count signals non-regenerative anemia, narrowing the search to kidney disease, bone marrow problems, or chronic illness.
From there, the workup depends on the suspected cause. Flea combs and fecal tests check for parasites. Blood smears can reveal damaged red blood cells characteristic of toxin exposure. Tests for FeLV and other infections help rule out infectious causes. Kidney values on a blood panel flag chronic kidney disease. In some cases, a bone marrow biopsy is needed to evaluate whether the marrow itself is the problem. Treatment always targets the underlying cause, because anemia in cats is almost always a symptom of something else rather than a standalone diagnosis.