Abstract
Most equine lower respiratory diseases present as increased airway neutrophilia, which can be detected in tracheal wash (TW) or bronchoalveolar lavage fluid (BALF) cytology samples. The aim was to compare the TW and BALF results in a population of client-owned horses with and without clinical respiratory disease signs. A secondary aim was to determine the sensitivity (Se) and specificity (Sp) of TW and BALF neutrophilia in detecting respiratory disease. The cutoff values for neutrophils were also evaluated. Retrospective data from 154 horses of various breeds that had been subject to both TW and bronchoalveolar lavage (BAL) sampling at rest during 2009−2015 were used. The horses were divided into three groups based on the presenting signs, physical examination, and endoscopy mucus score. Neutrophil counts of >20% in TW and >5% in BAL were considered abnormal. Cytology results between groups, correlations between TW and BALF cell types, and tracheal mucus score were analyzed. Two graph receiving operating characteristic (ROC) curves of the neutrophil percentage values of TW and BALF were created to determine the optimal cutoff values and to calculate the diagnostic Se and Sp for diagnosing airway inflammation in horses with and without clinical respiratory signs. The Se and Sp of TW and BALF neutrophil percentages were further estimated using a two-test one-population Bayesian latent class model. The two tests showed substantial agreement, and only 17.5% of the horses were classified differently (healthy vs. diseased). The neutrophil percentage was found to correlate between TW and BALF. The Se and Sp of TW were generally higher than for BAL when estimated with area under the curve or Bayesian model. Cutoff values of 17.7% for TW and 7% for BALF were indicated by the ROCs. We conclude that TW is a more sensitive and specific method in our patient population. We suggest that the current neutrophil cutoff values of 20% for TW and 5% for BALF would still be appropriate to use in clinical diagnosis of airway inflammation. However, further studies with other cell types and in other populations are warranted to determine the best sampling method for individual horses.
Highlights
Cytological analysis of tracheal wash (TW) and bronchoalveolar lavage fluid (BALF) is a common diagnostic procedure in equine practice when assessing the lower respiratory tract health of the horse [1, 2]
Clinical examination, airway endoscopy, and sample cytology, most horses of Group 3 were diagnosed with equine asthma [severe asthma (RAO; n = 25) and mild asthma (IAD; n = 7)], exercise induced pulmonary hemorrhage (EIPH; n = 1), other diagnosis related to respiratory tract (n = 8), and undetermined diagnosis (n = 1)
The seventy-nine horses in Group 2 had varying diagnoses including mild asthma (n = 40), severe asthma (n = 13), EIPH (n = 2), other diagnosis related to respiratory tract (n = 8), other diagnosis not related to respiratory tract (n = 6), and undetermined diagnosis (n = 10)
Summary
Cytological analysis of tracheal wash (TW) and bronchoalveolar lavage fluid (BALF) is a common diagnostic procedure in equine practice when assessing the lower respiratory tract health of the horse [1, 2]. TW is considered to give a better representation of the whole lung than bronchoalveolar lavage (BAL) and, often preferred in cases where an infectious disease is suspected because secretions from the affected lung areas will collect in the trachea [3]. BAL is recommended in suspected diffuse non-bacterial lung disease, and it is considered to be a more sensitive technique for detecting lower airway inflammation [2, 4]. In cases of uncertain etiology, performing both diagnostic tests simultaneously has been suggested in order to achieve accurate diagnosis [3, 5]
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