Effect of dithiothreitol on the differential cell count of equine tracheal wash aspirates

Potts, V., Pirie, S., McGorum, B., McGregor, G., Drumond, D. and Moss, S. (2019) Effect of dithiothreitol on the differential cell count of equine tracheal wash aspirates. British Equine Veterinary Association Congress 2019, Birmingham, UK, 11-14 Sept 2019. (doi: 10.1111/evj.43_13152)

Abstract

Background: Analysis of tracheal wash aspirates (TW) is a commonly applied diagnostic modality when investigating equine lower airway disease. In human respiratory medicine, the addition of a mucolytic agent following collection has been shown to increase diagnostic sensitivity, and quality of cytospin preparations [1]. Objectives: We hypothesised that the addition of the mucolytic dithiothreitol (DTT) to equine TW would: reduce background mucus superimposition, improve the ‘readability’ of cytospin preparations and significantly alter differential cell counts (DCC). Study design: Prospective cohort study. Methods: Forty-five TWs were collected from 31 horses, presenting either with respiratory clinical signs or for routine screening for lower airway inflammation. Prior to processing, one sample aliquot was treated with an equal volume of DTT and the paired aliquot left untreated. Samples were cytospun and stained using May-Grunwald € Giemsa. DCC and slide quality scores were calculated [1]. Paired data were compared (Wilcoxon rank test) and analysed for agreement (Bland–Altman plots). Significant airway inflammation was assumed beyond a threshold of 20% neutrophils. Results: DTT treatment significantly reduced background mucus staining grade (P = < 0.0001) and improved ‘readability’ of the preparations. No significant difference was found for neutrophil ratios (P = 0.9), with good agreement, between treated and untreated samples. Discounting cases with cytological evidence of bacterial infection, the addition of DTT did not significantly (Fishers exact; P = 0.2) alter the categorisation of cases. Main limitations: The majority of horses within this study population were classed as ‘normal’ on cytological examination. Improved understanding of the effect of DTT in horses with a greater degree of airway inflammation, would require a larger population of affected horses. Conclusions: Based on these results, addition of DTT facilitates cytological examination of tracheal wash cytospin preparations without altering the differential neutrophil percentage. Competing interests: None declared. Ethical animal research: Approval granted by the Veterinary Ethical Committee at the University of Edinburgh. Animal owners gave informed consent. Sources of funding: University of Edinburgh.

• Item Type: Conference or Workshop Item
• Status: Published
• Refereed: No
• Glasgow Author(s) Enlighten ID: de Boer, Mrs Valerie
• Authors: Potts, V., Pirie, S., McGorum, B., McGregor, G., Drumond, D., and Moss, S.
• College/School: College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Published Online: 14 September 2019