Lipid-laden macrophages in induced sputum are a marker of oropharyngeal reflux and possible gastric aspiration

The diagnostic properties of a "lipid index" of macrophages in induced sputum as a noninvasive marker of aspiration of acidic gastric contents were evaluated. In a cross-sectional study, 33 subjects (17 with symptoms suggestive of gastrooesophageal reflux) with normal chest radiographs and no symptoms of aspiration or sinus disease, underwent dual-channel 24-h ambulatory oesophageal pH recording and sputum induction. Oropharyngeal reflux, defined as at least one episode of a fall in pH to <4 at the upper oesophageal electrode, was considered indicative of aspiration of acidic gastric contents ("gold standard"). An index for the presence of intracellular lipid in sputum macrophages, detected by oil red O stain, was obtained. The sensitivity, specificity and predictive values of this "lipid index" were calculated. The "lipid index" could be calculated in 29 of 33 samples with high interobserver repeatability (intraclass correlation coefficient 0.96). Twenty subjects showed oropharyngeal reflux and nine did not. The median "lipid index" in subjects with oropharyngeal reflux (24.5) was significantly greater than that in those without reflux (1.0) (p<0.001). A "lipid index" of 7.0 had a sensitivity of 90%, a specificity of 89%, a positive predictive value of 95% and a negative predictive value of 80%. A "lipid index" of 7.0 in the macrophages of induced sputum is a good marker of oropharyngeal reflux.