Factors associated with clinical interpretation of tracheal wash fluid from dogs with respiratory disease: 281 cases (2012‐2017)

BACKGROUND: Clinicians face several dilemmas regarding tracheal washes (TWs) for the diagnosis of respiratory disease, including method and prediction of bacterial growth from cytology results. OBJECTIVE: To compare cytology and culture of endotracheal and transtracheal washes and identify factors associated with discordancy and bacterial growth. ANIMALS: Two hundred forty‐five dogs with respiratory disease. METHODS: Retrospective study. Tracheal wash submissions were included if cellularity was sufficient for cytologic interpretation and aerobic cultures were performed. Collection technique, cytology, bacterial growth, and antibiotic history were analyzed. RESULTS: Fewer transtracheal specimens (9/144, 6.3%) were excluded for hypocellularity than endotracheal (28/174, 16.1%); otherwise, results were similar and were combined. Of 281 specimens with cellularity sufficient for interpretation, 97 (34.5%) had bacteria on cytology and 191 (68.0%) had bacterial growth. Cytology positive/culture negative discordancy was uncommon (8/97, 8%). Cytology negative/culture positive discordancy was frequent (102/184, 55.4%), but occurred less often (28/184, 14.2%) when only 1+ growth or greater was considered positive. Oropharyngeal contamination was associated with bacterial growth, but not discordancy. No association was found between antibiotic administration and bacterial growth. CONCLUSIONS AND CLINICAL IMPORTANCE: Endotracheal wash fluid, in particular, should be screened for gross mucus or turbidity to maximize the likelihood of an adequate specimen. Otherwise, endotracheal and transtracheal specimens were similar. Presence of bacteria on cytology was a good predictor of any growth, while their absence was a good predictor of the absence of growth of 1+ or more. Recent antibiotic usage should not discourage TW culture if there is compelling reason to avoid delay.