A semiquantitative cytological evaluation of normal and pathological samples from the external ear canal of dogs and cats

Numbers of desquamated epithelial cells, yeast cells and bacterial organisms were counted in samples collected from the external ear canal of 37 normal dogs and 16 normal cats, and from 24 dogs and 22 cats with otitis externa. The aims of the study were to establish quantitative reference ranges and to correlate these data with the clinical status of the dogs and cats. Numbers of yeast cells and bacterial organisms were significantly increased in dogs (P = 0.05; P = 0.0001) and cats (P = 0.0001; P = 0.0001) with otitis externa, and in most cases high counts were correlated with clinical signs. Mean Malassezia counts per high-power dry field of greater than or equal to 5 in the dog and greater than or equal to 12 in the cat were considered abnormal. Mean bacterial counts per high-power dry field of greater than or equal to 25 in the dog and greater than or equal to 15 in the cat were considered abnormal. When used to differentiate normal from inflamed external ear canals, these figures provided a low sensitivity but a specificity of greater than or equal to 95%.