Relationships between equine airway reactivity measured by flowmetric plethysmography and specific indicators of airway inflammation in horses with suspected inflammatory airway disease

SummaryReasons for performing studyAgreement between airway reactivity measured by flowmetric plethysmography and histamine bronchoprovocation, and lower airway inflammation measured by bronchoalveolar lavage (BAL) cytology, has not been studied in horses with suspected inflammatory airway disease (IAD).ObjectivesWe tested the hypothesis that airway reactivity is associated withBALcytology in horses presenting for unexplained poor performance and/or chronic cough.Study designProspective clinical study.MethodsForty‐five horses, predominantly young Standardbred racehorses, presenting for unexplained poor performance or chronic cough, underwent endoscopic evaluation, tracheal wash, flowmetric plethysmography with histamine bronchoprovocation andBAL. Histamine response was measured by calculatingPC35, the concentration of nebulised histamine eliciting an increase in Δflowof 35%.ResultsIn this population, there was no significant correlation between histamine response and cell populations inBALcytology. When airway hyperreactivity (AHR) was defined as ≥35% increase in Δflowat a histamine concentration of <6 mg/ml, 24 of the 45 horses (53%) were determined to haveAHR. Thirty‐three (73%) had either abnormalBALcytology orAHR, and were diagnosed withIADon this basis. Of horses diagnosed withIAD, 9 (27%) had an abnormalBAL, 11 (33%) hadAHRand 13 (39%) had both.ConclusionsAirway reactivity andBALcytology did not show concordance in this population of horses presenting for unexplained poor performance and/or chronic cough. Failure to include tests of airway reactivity may lead to underdiagnosis ofIADin young Standardbred racehorses that present with clinical signs suggestive ofIAD.