Research on Immune-Mediated Hemolytic Anemia in Adult Equids

BUN might have utility as a prognostic indicator for IMHA/IMTP cases.
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horse laying down in stall filtered light

An article titled "Immune‐mediated hemolytic anemia and thrombocytopenia in 25 adult equids: 1997‐2016" was authored by Charlotte A. Easton‐Jones, Krista E. Estell and K. Gary Magdesian

This retrospective case-control study aimed to characterize the clinical presentation, clinicopathologic data, underlying conditions, treatment and outcome of immune‐mediated haemolytic anaemia (IMHA) and thrombocytopenia (IMTP) in horses. Horses were classified as primary or secondary IMHA/IMTP cases based on whether they had evidence of underlying infections, neoplasia or drug administration prior to the onset of clinical signs.

Twenty-four horses and one donkey met the inclusion criteria for cases. Two horses were diagnosed with IMHA only. Both horses were positive for anti-RBC antibodies on Coombs test. Eight equids were diagnosed with IMTP only and 15 were diagnosed with IMHA and concurrent thrombocytopenia. Controls were equids presented for non-immune‐mediated disease immediately prior to and after study animals.

Neoplasia incidence was significantly higher in the study population (28%) versus controls (8%). Overall short-term survival to discharge was 60%. There was no difference in survival between horses with IMHA, IMTP or both. Equids with primary disease were 13 times more likely to survive to discharge than those with secondary disease (8/9 vs 7/16). Treatment with corticosteroids, azathioprine or blood transfusions did not significantly affect outcome, although group numbers were small.

Survivors had a significantly lower blood urea nitrogen (BUN) than those that died or were subjected to euthanasia (survivors, 6.1 ± 2.5 mmol/L vs non- survivors, 9.9 ± 3.1 mmol/L). The odds of short-term mortality were also higher in horses presenting with increased BUN. Elevated BUN may act as a marker of the extent of hypoxic damage and severity of the immune-mediated disease.

Bottom line: Differentiation between primary and secondary etiologies can be challenging. Primary IMHA/IMTP cases have a reasonable prognosis and warrant treatment. Secondary cases have a poor prognosis and are frequently associated with a neoplastic process. BUN might have utility as a prognostic indicator for IMHA/IMTP cases.