RISK FACTORS FOR DEVELOPMENT OF IMHA – A PROSPECTIVE CASE‐CONTROL STUDY

Abstract

A prospective case‐control study was undertaken at DLEAH from May, 2001 to February, 2003 to examine risk factors for development of immune‐mediated hemolytic anemia (IMHA). A questionnaire was filled out by the attending doctor for each IMHA case diagnosed. The diagnosis of IMHA was made based on a PCV <25%, effective rule out of other diseases, and the presence of at least 2 of the following: spherocytosis; regenerative response with elevated reticulocytes or polychromasia; hemolysis characterized by bilirubinuria, hyperbilirubinemia, hemoglobinuria or hemoglobinemia; positive slide agglutination or positive Coombs' test. To provide case controls, the same questionnaire was filled out for the next canine patient admitted after diagnosis. Age, breed, vaccine history, previous illness, and medication history were examined. Date of admission was compared to total hospital case numbers to look for seasonality.The study contained 31 cases and 29 controls. Cases were significantly older than controls (7.45 years versus 5.1 years, p=0.01). Cocker spaniels and Cocker mixes were significantly more likely to be cases than controls (7/31 IMHA versus 1/29 controls, p=0.05). Medication and illness history for the 2 months prior to presentation was not significantly different between cases and controls. None of the IMHA cases had received antibiotics previously reported to be associated with IMHA. In contrast to previous studies, vaccination history was not significantly different between cases and controls. Five out of 31 cases had received vaccines in the previous 2 months; 4 of 9 controls had received vaccines in that same period. At least one case presented each month of the year. Although cases presented more frequently in the summer months, overall hospital case load was also elevated during these times. The monthly distributions of IMHA cases and total hospital case load were not significantly different.