Comparison of 4 fixation and staining methods for the cytologic evaluation of ear canals with clinical evidence of ceruminous otitis externa.
BACKGROUND
Swab cytology of ear canals is one of the most useful and rapid methods to assess the presence of external ear infections. Smears are generally stained with rapid Romanowsky-type stains, with or without prior heat fixation.


OBJECTIVE
The aim of this study was to compare 4 different methods of fixation and staining of ear swab cytology samples from dogs.


METHODS
Eight dogs with otitis externa were selected from a dermatology referral population. A cotton swab was used to obtain ceruminous material from 12 ear canals. Four smears of each swab were prepared on glass slides (randomly identified as A, B, C, or D) and air-dried for cytologic examination. Samples marked A were stained with Dip Quick (Jorgensen Laboratories Inc, Loveland, CO, USA) after heat fixation; samples marked B were stained without heat fixation; samples marked C were heat-fixed and dipped only in the counterstain (the blue reagent) of Dip Quick; and samples marked D were dipped only in the counterstain, without heat fixation. Ten high-power fields (hpf; X100 oil immersion objective) in each slide were evaluated by 2 observers, and total numbers of keratinocytes, yeast, bacteria, and neutrophils were counted. Statistical comparison was performed using an ANOVA model applied after verifying the normal distribution of the data, and using nonparametric sign tests and Wilcoxon signed rank tests.


RESULTS
No statistically significant differences were observed in the numbers of keratinocytes, yeast, bacteria, or neutrophils among the 4 staining methods (P > .05), although significant interobserver differences were found.


CONCLUSIONS
We conclude that heat fixation does not improve the quality of ceruminous ear swab samples for cytologic evaluation, and propose a 1-step dip in the blue reagent alone as a rapid method of staining samples from canine ear canals.
Toma
Stefano
S
Ospedale Veterinario Cuneese, Via Cuneo 52/N, 12011 Borgo S. Dalmazzo (CN), Italy.
Cornegliani
Luisa
L
Persico
Paola
P
Noli
Chiara
C
D000818:Animals; D001424:Bacterial Infections / Q000175:diagnosis / Q000662:veterinary; D002571:Cerumen / Q000166:cytology; D003881:Dermatomycoses / Q000175:diagnosis / Q000662:veterinary; D004283:Dog Diseases / Q000175:diagnosis* / Q000382:microbiology; D004285:Dogs; D004424:Ear Canal / Q000166:cytology*; D008290:Malassezia / Q000302:isolation & purification; D010032:Otitis Externa / Q000175:diagnosis / Q000382:microbiology / Q000662:veterinary*; D013048:Specimen Handling / Q000662:veterinary; D013194:Staining and Labeling / Q000379:methods / Q000662:veterinary*