Charcoal is a sensitive, specific, and stable marker for the diagnosis of aspiration in hamsters

The diagnosis of recurrent aspiration in young children is a perpetual challenge because there is no specific gold standard test to be used. The finding of lipid-laden alveolar macrophages in bronchoalveolar lavage (BAL) is a sensitive but nonspecific marker for the diagnosis of aspiration. We conducted a short-term study comparing tracheal instillation of saline, milk, or a milk-charcoal mixture in hamsters. BAL cytology, lipid-laden alveolar macrophage index, charcoal alveolar macrophage index, and lung histology were monitored for 10 d. A long-term study was performed, and hamsters were monitored for 92 d after milk-charcoal tracheal instillation. Baseline animals (n = 4) had no tracheal instillation. Saline- and milk-instilled animals had BAL performed after 1 (n = 4), 3 (n = 4), and 10 (n = 4) d. Milk-charcoal-instilled animals had BAL performed after 1 (n = 4), 3 (n = 4), 10 (n = 4), 30 (n = 2), 58 (n = 2), and 92 (n = 2) d after tracheal instillation. Total cell counts and percent neutrophils in BAL fluid increased significantly and similarly after milk and milk-charcoal instillation on d 1 compared with baseline and saline-instilled animals. Lipid-laden alveolar macrophage index increased significantly only on d 3 after milk and milk-charcoal instillation compared with all days in the saline-instillation group. Charcoal alveolar macrophage index increased significantly after milk-charcoal instillation (d 1-58) from baseline or all days in the saline-instillation group. We conclude that charcoal particles instilled in tracheas of hamsters can be easily identified in BAL fluid and in lung parenchyma for as long as 3 mo after a single instillation and could potentially be used as a sensitive, specific, and stable marker for the diagnosis of aspiration, although the issue of its applicability to humans is still unsolved.