Causes of Non-Regenerative Anemia in Cats: From Chronic Disease to Bone Marrow Disorders

Non-regenerative anemia in cats can result from decreased or ineffective erythropoiesis, while some disorders that shorten red blood cell survival can also present with a non-regenerative response. The differential list is broad, so prioritizing causes according to the individual patient is essential. 

Chronic Disease and Reduced Erythropoiesis 

Kidney disease is a common cause of feline non-regenerative anemia. Erythropoietin is produced primarily by the kidney, and both acute and chronic kidney disease can reduce its production^1,2. Inflammatory disease can also impair erythropoiesis through cytokine abnormalities and is commonly described as anemia of chronic disease. 

Other systemic conditions associated with non-regenerative anemia include inflammatory bowel disease, pancreatitis and hepatic lipidosis. Chronic blood loss can produce iron deficiency, particularly with gastrointestinal blood loss, severe flea infestation or chronic hematuria. As iron stores become depleted, progressive non-regenerative anemia can develop. 

In cats, conventional red cell indices may be relatively insensitive for detecting iron deficiency. Reticulocyte indices can provide additional information; decreased reticulocyte hemoglobin content (CHR <0.88 fmol) has been reported with 93.8% sensitivity and 76.9% specificity for identifying iron deficiency in cats³. 

Iron parameters can also help distinguish iron deficiency from anemia of inflammation. Serum iron may be low in both conditions, while ferritin is typically decreased with iron deficiency and increased with inflammation. TIBC is typically normal to increased in iron deficiency, although concurrent inflammation can complicate interpretation². 

Infectious and Drug-Associated Causes 

FeLV and FIV are among the most common infectious causes of feline non-regenerative anemia. Other infectious diseases reported in association with this pattern include FIP, Cytauxzoon felis, hemotrophic Mycoplasma species, Leishmania infantum, Ehrlichia canis and Mycobacterium species. 

Geography matters. Some infectious diseases are geographically specific, so the local disease profile and the cat’s travel history should be incorporated into the differential diagnosis. 

Medication and toxin exposure should also be reviewed. Reported drug-associated causes include chemotherapy and radiation therapy, propylthiouracil, methimazole, albendazole, ESAs, and certain antibiotics^2,4,5. 

When the Bone Marrow Is the Problem 

Primary and secondary bone marrow disorders can produce ineffective erythropoiesis. Important differentials include pure red cell aplasia (PRCA), non-regenerative immune-mediated hemolytic anemia (NRIMHA), aplastic anemia, myelodysplastic syndromes, myelofibrosis and myelophthisis. 

PRCA is characterized by a normocytic, normochromic, non-regenerative anemia without other cytopenias. Bone marrow examination shows decreased to absent red cell precursors⁶. 

NRIMHA can produce normocytic or macrocytic anemia, often accompanied by neutropenia or thrombocytopenia. The apparent macrocytosis may be caused by agglutination rather than reticulocytosis. Diagnostic support includes persistent agglutination after saline washing, a positive direct antiglobulin test, or ghost cells on a fresh blood smear^2,7. 

Aplastic anemia typically produces pancytopenia, with marked reduction or absence of normal hematopoietic tissue in the marrow, replaced by fat.4 Myelodysplastic syndromes commonly cause bicytopenia or pancytopenia and may show macrocytosis and dysplastic changes affecting all three cell lines². 

Myelofibrosis requires histopathologic confirmation with special staining, while myelophthisis results from infiltration and replacement of normal marrow space by abnormal cells². 

^{Practical Clinical Takeaway} 

A cat with non-regenerative anemia should not automatically be assigned a single explanation such as chronic kidney disease. Common systemic, infectious, nutritional, drug-associated and marrow-related causes all warrant consideration according to the patient’s presentation. When routine testing does not explain the anemia, bone marrow evaluation can become essential for distinguishing these conditions and directing treatment. 

References 

1. Furman E, Leidinger E, Hooijberg EH, Bauer N, Beddies G, Moritz A. A retrospective study of 1,098 blood samples with anemia from adult cats: frequency, classification, and association with serum creatinine concentration. Journal of veterinary internal medicine. 2014 Sep;28(5):1391-7. https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/jvim.12422 

2. Winzelberg Olson S, Hohenhaus AE. Feline non-regenerative anemia: Diagnostic and treatment recommendations. Journal of feline medicine and surgery. 2019 Jul;21(7):615-31. https://journals.sagepub.com/doi/pdf/10.1177/1098612X19856178 

3. Prins M, Van Leeuwen MW, Teske E. Stability and reproducibility of ADVIA 120-measured red blood cell and platelet parameters in dogs, cats, and horses, and the use of reticulocyte haemoglobin content (CH (R)) in the diagnosis of iron deficiency. Tijdschrift voor diergeneeskunde. 2009;134:272-8. https://research-portal.uu.nl/ws/files/15405423/2009_Prins_TvDl_ADVIA_120.pdf 

4. Black V, Adamantos S, Barfield D, Tasker S. Feline non-regenerative immune-mediated anaemia: features and outcome in 15 cases. Journal of feline medicine and surgery. 2016 Aug;18(8):597-602. https://journals.sagepub.com/doi/pdf/10.1177/1098612X15588800 

5. Chalhoub S, Langston CE, Farrelly J. The use of darbepoetin to stimulate erythropoiesis in anemia of chronic kidney disease in cats: 25 cases. Journal of veterinary internal medicine. 2012 Mar;26(2):363-9. https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1939-1676.2011.00864.x 

6. Viviano KR, Webb JL. Clinical use of cyclosporine as an adjunctive therapy in the management of feline idiopathic pure red cell aplasia. Journal of Feline Medicine and Surgery. 2011 Dec;13(12):885-95. https://journals.sagepub.com/doi/pdf/10.1016/j.jfms.2011.07.007 

7. Swann JW, Szladovits B, Glanemann B. Demographic characteristics, survival and prognostic factors for mortality in cats with primary immune-mediated hemolytic anemia. Journal of veterinary internal medicine. 2016 Jan;30(1):147-56. https://academic.oup.com/jvim/article-pdf/30/1/147/66689783/jvim13658.pdf