Consider BAL in Both Lungs when Evaluating Airway Disease

No two lungs are exactly alike—especially when it comes to equine airway disease. According to French researchers, when investigating lung conditions using bronchoalveolar lavage (BAL), ensure you’re checking both lungs in the process.

BAL is a diagnostic tool used to evaluate equine lung conditions that involves injecting a horse’s lung with sterile fluid before drawing it back out again for analysis. The current practice is to “wash” just one of the horse’s lungs. But limiting the BAL to a single lung can lead to missed diagnoses and false negatives, said Marianne Depecker, a PhD candidate at the animal physiopathology and functional pharmacology department at the University of Nantes-Angers-Le Mans, in Nantes, France. She presented study results on the topic at the French Equine Research Day, held February 28 in Paris.

“A BAL procedure will effectively represent the entire sampled lung, but one sampled lung is not representative of the other,” she said.

Depecker and colleagues performed bilateral BALs in 138 French Standardbred harness racing horses—the largest population of BAL research horses to date. Comparing samples from both lungs of each horse, they found significant differences from one lung to another within individual horses.

On the whole, they found that the right lung tended to have larger percentages of neutrophils (a kind of white blood cell) and hemosiderophages (macrophages, another kind of white blood cell, that have ingested red blood cells from previous pulmonary hemorrhage) than the left lung, Depecker said. The right lung also had higher hemosiderophage-to-macrophage ratios, she said; if hemosiderophages represent at least 20% of all macrophages, it's a sign that the horse has been bleeding in the lungs.

“It seems apparent that sampling both lungs is indicated when performing BAL,” Depecker said.

If it’s only possible to sample one lung, Depecker suggested veterinarians choose the right lung, which has a tendency to reveal stronger concentrations of the cells in question, she added. “But if only one lung is tested, less restrictive thresholds should be used than those previously described for diagnosing inflammatory airway disease, so as to limit the number of false negatives coming from a single biopsy,” she said. “The risk of incorrectly considering a horse ‘healthy’ increases with the use of restrictive thresholds for the cellular populations studied, as well as when the BAL is performed in the left lobe only."

Welfare concerns about carrying out a double BAL—which many clinicians consider to be more unpleasant for the humans watching the procedure than for the horse experiencing it—should not deter handlers from following the protocol, Depecker added. “In our study the vast majority of the horses tolerated the procedure very well, and only a handful had to be sedated,” she said.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.