FrançaisWhat destroys red cells in cats
| Cause | What happens | To know |
|---|---|---|
| Primary IMHA | The immune system attacks the cat’s own red cells, with no cause found | Most often young adult cats, aged about 2 to 6 years [3]. |
| Secondary IMHA | Another disease triggers the immune attack | Strong evidence for Mycoplasma haemofelis; FeLV and Babesia felis are also implicated [1]. |
| Oxidative damage (Heinz bodies) | Toxins damage hemoglobin, which clumps inside the cells | Onion and paracetamol (acetaminophen) are classic causes [7, 9]. |
| Pyruvate kinase (PK) deficiency | An inherited enzyme defect shortens red cell life | Abyssinians and Somalis above all; some affected cats show no signs [10, 11]. |
| Neonatal isoerythrolysis | Kittens absorb anti-A antibodies from a type B mother’s first milk | Signs within hours to days of birth; high mortality [12]. |
For anemia in general, including blood loss and low production, see anemia in cats. The dog version of the immune form is covered in IMHA in dogs.
What the blood work shows
- PCV or hematocrit: often severely low. In 19 cats with primary IMHA, the PCV on admission was 6 to 22%, with a median of 12% [2].
- Aggregate reticulocytes: the young red cells that show the marrow is answering now [5]. The marrow needs 3 to 5 days, and in one study more than half the cats with primary IMHA were not yet regenerative on arrival; many became so later [3, 5].
- Agglutination: red cells stuck together in clumps. Clumps that persist when blood is mixed with saline are good evidence of antibodies on the cells [1].
- Spherocytes: small round red cells that help diagnose IMHA in dogs, but not in cats, because normal feline red cells are small and often lack a pale center [1, 3].
- Heinz bodies: small ones occur in many healthy cats and more in cats with diabetes, lymphoma or hyperthyroidism; many large ones with eccentrocytes point to oxidative damage [7].
- Bilirubin: red cell breakdown raises bilirubin and can cause jaundice. In cats, any bilirubin in the urine is abnormal [1, 8]. In primary IMHA, 13 of 19 cats had a high bilirubin [2].
- Globulins and lymphocytes were often high in cats with primary IMHA, a feature not typical of dogs [2, 3].
Bilirubin and urine changes are also explained in urinalysis for dogs and cats.
How to read the PCV line
Here is an illustrative line from a pale, weak cat with red cell destruction.
- Abbreviation PCV, HCT or Ht: the share of the blood made of red cells.
- Result 12% in this example, the median PCV on admission in 19 cats with primary IMHA [2].
- Unit Percent; some machines print a fraction (0.12 L/L).
- Laboratory interval An example interval for cats; each laboratory sets its own.
- Flag L: below the interval. Read it with the aggregate reticulocytes: below about 61,000/µL (61 ×10⁹/L) the response is inadequate, while a high count fits destruction or loss of red cells [5, 6].
How vets confirm hemolysis and find the cause
- Saline agglutination test: one drop of blood with four drops of saline; clumps that persist, if needed after washing the cells, support IMHA [1].
- Coombs test (direct antiglobulin test): looks for antibodies on the red cells. In one study it was negative in healthy and non-anemic sick cats and positive in 18 anemic cats, most with primary IMHA [2]. A firm diagnosis needs two signs of immune destruction, or saline agglutination that persists after washing, plus a sign of hemolysis [1].
- Mycoplasma PCR for M. haemofelis in every cat with IMHA [1]. See Mycoplasma haemofelis in cats.
- FeLV and FIV tests in every sick cat [1]. A positive in-clinic FeLV test can be falsely positive in cats with immune anemia, so a PCR helps confirm it [13]. See FeLV and FIV in cats.
- A smear stained with new methylene blue shows Heinz bodies clearly [7]. Ask about access to onion, garlic or human painkillers.
- Blood typing of the queen and kittens confirms neonatal isoerythrolysis [12]; a DNA test confirms PK deficiency [11].
Toxins, inherited disease and newborn kittens
Onion and paracetamol. Onion, garlic and related plants cause Heinz bodies and methemoglobin, and cooking or drying does not remove the toxic effect [9]. Cats are highly susceptible [9]. Cats also lack a key liver enzyme for clearing paracetamol (acetaminophen) and aspirin, which makes them remarkably sensitive to these drugs [14]. See onion and garlic toxicity.
PK deficiency. In 25 affected Abyssinian and Somali cats, 70% were anemic and 94% had high aggregate reticulocytes; 11 cats showed no signs at all [10]. Testing before breeding is recommended, and the mutation also occurs in other breeds such as Bengals and Maine Coons [10, 11]. See the Abyssinian.
Neonatal isoerythrolysis. Type B cats naturally carry antibodies against type A red cells. Type A kittens born to a type B mother are healthy at birth, then absorb these antibodies from colostrum: dark red-brown urine, jaundice, anemia and death in the first week can follow [12]. Type B is common in some breeds, for example about 41% of Devon Rex and 36% of British Shorthair cats in one compilation [12].
Outlook
Primary IMHA has a better outlook in cats than in dogs [2]. In 107 cats, median survival was 516 days with primary IMHA but 14 days with IMHA secondary to another disease; 59% of cats with primary IMHA were alive at 6 months, against 26% of secondary cases [3]. A higher bilirubin and older age were linked to a worse outlook [3].
In a 2026 study of 37 cats, 24% died, all within the first four weeks. Most survivors needed long treatment, and lasting remission without treatment was uncommon [4]. Relapses occurred in 31% of cats in an earlier study [2].
Related articles
En français : anémie hémolytique du chat.
Questions to ask your veterinarian
- How low is the PCV, and are aggregate reticulocytes rising?
- Is there agglutination in saline, and should a Coombs test be done?
- Has a Mycoplasma PCR been done, and what were the FeLV and FIV results?
- Are there Heinz bodies on the smear, and could a toxin be involved?
- Is this primary or secondary, and what does that mean for the outlook?
Get your cat’s blood count explained, line by line.
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Frequently asked questions
How bad is anemia in cats?
It depends on the cause and severity. Hemolytic anemia can be severe: in 19 cats with primary IMHA, the median PCV on admission was 12% [2]. Cats with primary IMHA had a median survival of 516 days, but only 14 days when IMHA was caused by another disease [3].
Can hemolytic anemia go away on its own?
When another disease causes it, treating that disease can stop the destruction; for example, IMHA from Babesia felis resolved with treatment of the infection alone [1]. Primary IMHA usually needs long treatment, and lasting remission without treatment is uncommon [4].
What can trigger hemolytic anemia in cats?
Infections such as Mycoplasma haemofelis, FeLV and Babesia felis [1], toxins such as onion and paracetamol [7, 9], inherited PK deficiency [10] and, in newborn kittens, a blood type mismatch with the mother [12].
Sources
- Garden OA et al. ACVIM consensus statement on the diagnosis of immune-mediated hemolytic anemia in dogs and cats. J Vet Intern Med. 2019;33(2):313-334. doi.org/10.1111/jvim.15441
- Kohn B et al. Primary immune-mediated hemolytic anemia in 19 cats: diagnosis, therapy, and outcome (1998-2004). J Vet Intern Med. 2006;20(1):159-166. pubmed.ncbi.nlm.nih.gov/16496936
- Swann JW et al. Demographic characteristics, survival and prognostic factors for mortality in cats with primary immune-mediated hemolytic anemia. J Vet Intern Med. 2016;30(1):147-156. doi.org/10.1111/jvim.13658
- Kulmer LM et al. Clinical findings, treatment and long-term outcome in 37 cats with non-associative immune-mediated hemolytic anemia. Animals (Basel). 2026;16(17):2727. doi.org/10.3390/ani16172727
- eClinPath, Cornell University College of Veterinary Medicine. Assessment of regeneration. eclinpath.com/hematology/anemia/assessment-regeneration
- eClinPath, Cornell University College of Veterinary Medicine. Absolute reticulocyte count. eclinpath.com/hematology/tests/absolute-reticulocyte-count
- eClinPath, Cornell University College of Veterinary Medicine. Red blood cell inclusions. eclinpath.com/hematology/morphologic-features/red-blood-cells/rbc-inclusions
- eClinPath, Cornell University College of Veterinary Medicine. Bilirubin. eclinpath.com/chemistry/liver/cholestasis/bilirubin
- Cortinovis C, Caloni F. Household food items toxic to dogs and cats. Front Vet Sci. 2016;3:26. doi.org/10.3389/fvets.2016.00026
- Kohn B, Fumi C. Clinical course of pyruvate kinase deficiency in Abyssinian and Somali cats. J Feline Med Surg. 2008;10(2):145-153. doi.org/10.1016/j.jfms.2007.09.006
- Grahn RA et al. Erythrocyte pyruvate kinase deficiency mutation identified in multiple breeds of domestic cats. BMC Vet Res. 2012;8:207. doi.org/10.1186/1746-6148-8-207
- Silvestre-Ferreira AC, Pastor J. Feline neonatal isoerythrolysis and the importance of feline blood types. Vet Med Int. 2010;2010:753726. doi.org/10.4061/2010/753726
- Robert LI et al. A retrospective review of cats with suspected false positive results in point-of-care feline leukemia virus tests and concurrent immune-mediated anemia. J Am Vet Med Assoc. 2023;261(10):1459-1465. doi.org/10.2460/javma.23.02.0059
- Shrestha B et al. Evolution of a major drug metabolizing enzyme defect in the domestic cat and other felidae: phylogenetic timing and the role of hypercarnivory. PLoS One. 2011;6(3):e18046. doi.org/10.1371/journal.pone.0018046
Laboratory methods and reference intervals vary. This article explains; it does not diagnose. For a decision about your pet, use the original report and talk to your veterinarian. Our editorial policy.