How many cells should be counted when performing a differential count on bovine non-bronchoscopic bronchoalveolar lavage fluid?

Objectives: Noninfectious airway inflammation, for example, due to high levels of particulate matter, can predispose to airway infection. The most accessible method to assess airway inflammation in living animals is cytologic analysis of bronchoalveolar lavage fluid. However, this is a labor-intensive method due to the high number of cells ideally included in the differential count. Therefore, the objective of this study was to determine if counting 300 cells would yield comparable results compared to 500 cells. Materials and methods: Differential counts based on 300 and 500 cells were performed on 134 Hemacolor stained, cytospin preparations. Bland-Altman plots and calculation of beta gamma tolerance intervals were performed. For lymphocytes, bootstrapping was implemented to account for the non-normal distribution. The maximal acceptable difference was set at 5% for macrophages and neutrophils, and 2.5% for lymphocytes. Results: By the calculation of beta gamma tolerance interval it was predicted with 90% certainty that 95% of future results would lie in the interval of -3.99% to 3.76% for macrophages, -3.39% to 3.74% for neutrophils, -1.78% to 1.62% for lymphocytes. Tolerance intervals were not calculated for eosinophils due to their distribution and a slight proportional bias. The maximum observed difference was 1.13%. Conclusions: For diagnostic purposes, macrophages, neutrophils and lymphocytes enumeration based on 300 cells seems a reliable and less time-consuming alternative in comparison to the 500 cell differential count.