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Routine haematology and biochemistry are usually within normal limits, and there is little evidence to support the use of serum and intradermal allergy testing in the diagnosis of RAO^allen.

Routine haematology and biochemistry are usually within normal limits, and there is little evidence to support the use of serum and intradermal allergy testing in the diagnosis of RAO^allen.

Fluids obtained from bronchoalveolar lavage or tracheal wash may be useful in the diagnosis of RAO.

Fluids obtained from bronchoalveolar lavage or tracheal wash may be useful in the diagnosis of RAO. The presence of greater than 20% neutrophils in BALF confirms the presence of lower airway inflammation, thus and differentiates horses with RAO from those with eosinophilic pneumonitis, fungal pneumonia, or lungworm infestation. Normal horses have fewer than 10% neutrophils in BALF. Cytology of bronchoalveolar lavage fluid may also reveal Curschmann’s spirals , which represent inspissated mucus/cellular casts from obstructed small airways¹. BAL should not be performed if the horse is markedly dyspnoeic and should be postponed until the dyspnoea is controlled. There  

Bronchoalveolar lavage is rarely required for diagnosis of fulminant RAO, and is not innocuous in horses that are dyspneic at rest. It is indicated in horses with mild to moderate disease with poor performance and coughing during exercise. Neutrophilic inflammation (20-90% of total cell count) confirms the presence of lower airway inflammation and differentiates horses with eosinophilic pneumonitis, fungal pneumonia, or lungworm infestation from horses with heaves. Curschmann’s spirals may be observed on cytologic evaluation and represent inspissated mucus/cellular casts from obstructed small airways

The severity of lung inflammation can be evaluated by cytological evaluation of bronchoalveolar lavage fluid (BALF; see chapter by Viel and Hewson for lavage and cytology techniques). In normal horses, lymphocytes and macrophages form the majority of cells in BALF and neutrophils comprise less than ten percent of cells. In horses with RAO or SPAOD, there is an increase in the percentage of neutrophils and, in severely affected animals, neutrophils comprise over 50 percent of cells and are not degenerate. Despite the large number of neutrophils in BALF, there is no evidence of bacterial infection.

BAL should not be performed

if the horse is markedly dyspnoeic and should be

postponed until the dyspnoea is controlled. There  

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