Primary Immuno-mediated-hemolytic anemia: a retrospective study of 52 dogs from two veterinary teaching hospitals

Primary immune-mediated hemolytic anemia (pIMHA) is a type II hypersensitivity (antibody-dependent cytotoxicity), and is the most common immunehematologic disorder in dogs. It leads mostly to moderate to severe anemia, with subsequent hypoxemia, hypercoagulability, and often fatal outcomes. This retrospective study (2009-2015) examined the clinical and laboratory findings at the presentation visit in dogs with pIMHA, in two veterinary teaching hospitals (Pisa, Italy; Koret, Israel). The study included 52 dogs (Pisa n = 30; Koret n = 22) presented with hematocrit < 30%, combined with ≥ 1 of the following: spherocytosis, positive osmotic fragility test, autoagglutination, positive Coombs' test or positive flow cytometry for RBC-bound IgG and/or IgM. Cases were excluded if positive to tick-borne disease or other infections, based on serology or PCR assay, or if diagnosed with systemic neoplasia. Data retrieved from medical records included the signalment, clinical and laboratory findings. Data regarding gender and breed in the Pisa group was compared with a control population, which included all dogs presented to the Pisa hospital during the study period (n = 19,647). The findings in Pisa and Koret groups were compared. Dogs with pIMHA were mainly middle-aged to elderly dogs, presented with no seasonal pattern. In the Pisa group, neutered females (p = 0.021), as well as Cocker-Spaniel and Maltese dogs (p = 0.025 and p = 0.012, respectively) were overrepresented compared to the control population. The most frequent clinical signs included pale mucous membranes and lethargy (88% each), anorexia (65%), tachycardia (42%), tachypnea (38%), and pigmenturia (35%). The Koret dogs were significantly more icteric, tachycardic and tachypneic compared to the Pisa dogs (p = 0.048, p = 0.017 and p = 0.001, respectively). Anemia was classified as macrocytic-hypochromic (43%), macrocytic-normochromic (27%), macrocytic-hyperchromic (12%), normocytic-normochromic (10%), normocytic hypochromic and normocytic-hyperchromic (4% each). The Koret group had significantly more dogs with anemia classified as hyperchromic (p = 0.001), suggesting higher frequency of hemoglobinemia due to intravascular hemolysis. The common morphological cellular blood anomalies included polychromasia (94%), anisocytosis and metarubricytosis (82% each), spherocytosis and leukocytosis (80% each), neutrophilia (69%), Howell-Jolly bodies and left-shift (49% each), macrothrombocythemia (45%), thrombocytopenia (35%), monocytosis (31%), autoagglutination (27%), hypochromia (16%), poikilocytosis (16%), and schistocytosis (14%). This study confirms previous findings regarding the signalment, clinical and laboratory characteristics of pIMHA in dogs. The microscopic evaluation of the blood smear is a valuable tool in the diagnosis of pIMHA. The Koret group was characterized by a more severe presentation of the disease, likely because this hospital admits more emergency primary care cases.