Daily Vet Life 71: An Anaphylaxis Emergency

Dr. Rana Buzorgmanesh shares a rare and complex case of anaphylaxis in a 16-year-old paint mare that initially presented with colic signs but was ultimately diagnosed with primary polycythemia secondary to a severe vaccine reaction. Despite standard colic workups showing no gastrointestinal cause, the mare exhibited dangerously high hematocrit levels (PCV 77) and rising creatinine, indicating azotemia. After ruling out primary neoplasia via bone marrow aspirate and considering the timeline post-vaccination, the team hypothesized that anaphylaxis triggered hyperviscosity syndrome, leading to kidney dysfunction. Treatment was unconventional: eight liters of blood were removed via controlled phlebotomy while administering IV fluids, supplemented with antihistamines (hydroxyzine and H2 blocker), clopidogrel for anticoagulation, and cautious avoidance of steroids due to laminitis risk. The mare responded dramatically, with normalized blood work and recovery within a week. The case highlights the importance of systematic differential diagnosis, not dismissing unusual presentations, and the value of advanced diagnostics and creative treatment in equine critical care. The mare remains healthy over a year later, with future vaccination managed through titer testing and hospital monitoring.