Letter regarding “Effect of dilution of canine blood samples on the specificity of saline agglutination tests for immune‐mediated hemolysis,” original and modified saline agglutination tests vs direct Coombs’ tests

Immune‐mediated hemolytic anemia (IMHA) is an important cause of morbidity and mortality in dogs. IMHA also occurs in cats, although less commonly. IMHA is considered secondary when it can be attributed to an underlying disease, and as primary (idiopathic) if no cause is found. Eliminating diseases that cause IMHA may attenuate or stop immune‐mediated erythrocyte destruction, and adverse consequences of long‐term immunosuppressive treatment can be avoided. Infections, cancer, drugs, vaccines, and inflammatory processes may be underlying causes of IMHA. Evidence for these comorbidities has not been systematically evaluated, rendering evidence‐based decisions difficult. We identified and extracted data from studies published in the veterinary literature and developed a novel tool for evaluation of evidence quality, using it to assess study design, diagnostic criteria for IMHA, comorbidities, and causality. Succinct evidence summary statements were written, along with screening recommendations. Statements were refined by conducting 3 iterations of Delphi review with panel and task force members. Commentary was solicited from several professional bodies to maximize clinical applicability before the recommendations were submitted. The resulting document is intended to provide clinical guidelines for diagnosis of, and underlying disease screening for, IMHA in dogs and cats. These should be implemented with consideration of animal, owner, and geographical factors.

Background Difficulties with the direct antiglobulin test (DAT) and its apparent lack of sensitivity and specificity for immune‐mediated hemolytic anemia (IMHA) in dogs have raised skepticism regarding its diagnostic value. Objective To compare different DATs and other hematologic parameters in dogs. Animals Anticoagulated blood samples from 59 nonanemic and 46 anemic dogs (± IMHA) from a research colony and veterinary clinics. Methods Prospective observational study: Immunochromatographic strip, gel microcolumn, and capillary techniques were compared with standard microtiter DAT using 2 polyvalent antiglobulins. Spherocytosis, autoagglutination, osmotic fragility, and clinical data were assessed. Results Blood samples from all 59 nonanemic dogs were DAT‐. Among 46 anemic dogs, 33 were suspected of IMHA, but only 20 were DAT+. Old and new DAT methods yielded comparable and consistent results even after storage of chilled blood samples for 1 week. Spherocytosis and autoagglutination (that did not persist after washing) were noted in 15 and 16 DAT+ dogs, respectively. The other 26 anemic dogs, including 21 previously transfused dogs and 4 with autoagglutination, tested DAT‐ by the other methods. Osmotic fragility was increased in 70% (19/27) of anemic and all 15 DAT+ dogs tested. Limited follow‐up testing revealed DAT+ results for 3–70 days. Conclusions and Clinical Importance The novel strip and capillary DAT methods are promising adjunct in‐clinic tools. Despite prior immunosuppressive treatment and presence of autoagglutination, the DAT was positive in anemic dogs with IMHA. Transfusion did not cause false DAT+ results. Our results support DAT as a cornerstone in the diagnosis of canine IMHA.

A definitive diagnosis of immune-mediated hemolytic anemia (IMHA) can be difficult to make. However, it is critical to differentiate IMHA from other causes of anemia due to the impact on prognosis and outcome for IMHA patients. Recently published American College of Veterinary Internal Medicine recommendations for the diagnosis of IMHA should be followed to concurrently confirm ongoing anemia, verify in vivo hemolysis, and detect anti-erythrocyte antibodies. The reliability of immunologic IMHA tests varies depending on which test is used and how it is performed.