Comparison of tracheal aspirates and bronchoalveolar lavage in racehorses 2. Evaluation of the diagnostic significance of neutrophil percentage

Objective To determine whether diagnosis of airway inflammation, using cut‐off percentages for neutrophils, differs when based on samples from tracheal aspirate (TA) and bron‐choalveolar lavage (BAL) collected concomitantly from the same racehorse. Design Retrospective case series of 48 young Thoroughbred and Standardbred racehorses in race training, but showing poor performance. Procedure TA and BAL samples were collected from all horses 1 to 2 h after high‐speed treadmill exercise. Aliquots of the retrieved fluid were cytocentrifuged and smears stained with Diff‐Quik®. The mean percentage of neutrophils was calculated. Diagnostic cut‐off points were set at 20% for TA samples and 5% for BAL samples. Agreement in the interpretations between the two techniques was analysed. Results In 19 of 51 paired samples (37%) there were differences in diagnostic interpretation between TA and BAL samples. Of these, airway inflammation was indicated only by the TA sample in 13 and only by the BAL in 6. Conclusion TA and BAL samples give important information about different regions of the airway, but neither should be used alone for the diagnosis of inflammation of the entire lung. The limitations of these procedures mean that both samples should be collected when it is desired to cytologically evaluate the entire lower airway.