Comparison of four staining methods for detection of mast cells in equine bronchoalveolar lavage fluid.
Authors: Leclere Mathilde, Desnoyers Michel, Beauchamp Guy, Lavoie Jean-Pierre
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary Mast cell percentages in bronchoalveolar lavage fluid are considered clinically significant markers of airway inflammation in horses, yet substantial variability between published studies suggests methodological inconsistencies in their detection. Leclere and colleagues compared four staining approaches on BALF samples from 24 horses, counting 400 cells per slide and analysing mast cell percentages using repeated-measures ANOVA and Bland-Altman agreement assessment. The fast Romanowsky method significantly underestimated mast cells (relying on morphology alone, as granules remained unstained), whilst toluidine blue produced the highest counts but proved unsuitable for concurrent differential counts of other cell types; by contrast, automated Romanowsky and May-Grünwald Giemsa stains provided reliable metachromatic visualisation of mast cell granules and maintained diagnostic utility for the broader cell population. These findings highlight why mast cell reference ranges and clinical thresholds have differed inconsistently across equine literature—staining methodology directly impacts reported prevalence—and underscore the need for standardised protocols in respiratory diagnostics. Practitioners interpreting BALF results should establish whether their laboratory uses metachromatic staining, as fast Romanowsky alone may miss clinically relevant mast cell elevations associated with inflammatory airway disease.
Read the full abstract on PubMed
Practical Takeaways
- •When submitting BALF samples for mast cell analysis, ensure your laboratory uses automated Romanowsky, May-Grünwald Giemsa, or toluidine blue staining rather than fast Romanowsky methods to avoid falsely low mast cell counts that could miss clinically relevant airway inflammation
- •Mast cell percentages vary significantly depending on staining method used, so results from different laboratories may not be directly comparable; establish reference ranges specific to your diagnostic laboratory's staining protocol
- •If investigating suspected inflammatory airway disease in performance horses, request specific staining methods that visualize mast cell granules metachromatically rather than relying on morphologic identification alone
Key Findings
- •Fast Romanowsky stain significantly underestimated mast cell percentages in equine BALF because metachromatic granules were not stained
- •Toluidine blue staining detected the highest mean percentage of mast cells with visible metachromatic granules, but was inadequate for differential cell counts of other cell types
- •Automated Romanowsky and May-Grünwald Giemsa stains provided reliable metachromatic staining of mast cell granules comparable to toluidine blue
- •Mast cell identification based on morphologic criteria alone (fast Romanowsky) is unreliable compared to granule-specific staining methods