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

Abstract

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.

Induced sputum cell counts: their usefulness in clinical practice

“…The demonstration of lipid in macrophages can be an indicator of aspiration of gastric contents and the examination of BAL for lipid laden macrophages has been suggested as a useful diagnostic test for aspiration [73,74]. Recently, the examination of induced sputum for lipid laden macrophages was shown to have high sensitivity (90%) and specificity (89%) for oropharyngeal reflux measured by 24-h dual channel oesophageal pH monitoring, for an alveolar macrophage lipid laden index of 7.0 [75] ( fig. 3c).…”

“…An intense neutrophilia with elevation of total cell count and the proportion of neutrophils, would suggest an infective bronchitis [55], bronchiectasis [80] or another cause for this such as cystic fibrosis. On the other hand, if the sputum cell counts are normal or if there is a neutrophilia with a normal total cell count, other conditions such as gastroesophageal reflux [75], habit cough need to be considered.…”

Application of Immunocytochemistry to Sputum Cells to Investigate Molecular Mechanisms of Airway Inflammation

“…Since the total cell count could be lessened after centrifugation (Parameswaran, et al 2000, Rerecich, et al 1999, it is therefore recommended that total cell count be performed prior to centrifugation to exactly obtain the original cell count. The currently automated machine is not reliable for determining total cell count and differential cell count, and is still not recommended.…”

Clinical applications of assessment of airway inflammation using induced sputum

“…Further work is required to determine the sputum cell characteristics of cough associated with gastro-oesophageal reflux, rhinitis and viral infections, although a recent bronchoscopic study suggests that no particular patterns will emerge [22]. Lipid-laden macrophages are noted more commonly in induced sputum from patients with oropharyngeal reflux than controls, suggesting that this might be a useful noninvasive marker of oropharyngeal reflux with gastric aspiration [23]. Patients with cough and sputum eosinophilia exhibit an objective response to corticosteroid treatment that occurs in parallel with a treatment-associated fall in the sputum eosinophil count [20,24].…”