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Bronchoalveolar lavage (BAL) and thoracic radiography are routinely performed procedures in the diagnostic work-up of equine chronic respiratory disease. The objective of this study was to evaluate the influence of standardized BAL on thoracic radiographs in a referral-hospital population compared to healthy controls, in which caudoventral and caudodorsal radiographs of the thorax were taken before and after BAL. Based on the results of the clinical examination, blood gas analysis, bronchoscopy, BAL
cytology and thoracic radiography 53 horses were available for study including 12 healthy controls and 41 horses affected by chronic respiratory disease: recurrent airway obstruction (RAO, n = 12), inflammatory airway disease (IAD, n = 21) and chronic interstitial pneumopathy (CIP, n = 6). Caudoventral and caudodorsal radiographs were obtained from all horses before and within 30 min after BAL, blinded, randomized and interpreted by three independent observers. The ability of observers to correctly identify the time point of the radiograph (before or after BAL) was significantly influenced by clinical diagnosis and projection. Based on a logistic mixed model, the chance (adjusted odds) of misinterpretation of the correct time point was about 3 times higher in radiographs of RAO horses when compared to healthy controls (OR = 3.13, P = 0.019). No significant differences were found for IAD and CIP. The chance of misinterpretation of the
correct time point was about 3 times lower in caudo-dorsal projections than in caudoventral projections (OR = 0.232, P < 0.001). In conclusion, the results of the study lead to the recommendation to perform BAL after thoracic radiography, although radiographic
quality might only be affected in minor disease.