Aims Demonstration of lipid-laden macrophages in respiratory secretions has been suggested to be a marker of reflux and aspiration. However studies looking at the diagnostic value of quantifying macrophage ingested lipids have been inconclusive. We wanted to look evaluate the utility of this technique in diagnosing airway reflux.
Methods In this prospective study bronchoalveolar lavage samples were collected from patient’s undergoing flexible bronchoscopy for various indications (lung cancer, chronic cough, ILD etc). Cells collected were stained with Oil-Red-O. Lipid-laden macrophage index (LLMI) was used to quantify lipid accumulation. This is calculated by grading the amount of intracellular Oil-Red-O positive particles per 100 alveolar macrophages. A score of 0 (no opacification) to 4 (total opacification) is assigned to each macrophage. The sum of the scores yields the LLMI. Patients were asked to complete the Hull Airways Reflux Questionnaire (HARQ), a validated tool to diagnose airways reflux. One of the investigators, blind to the analysis, independently reviewed the clinical notes to establish a diagnosis of associated airway reflux. The investigator performing cell analysis was blind to the clinical details. The groups with and without a clinical diagnosis of airway reflux were compared. Correlations between the HARQ score and LLMI were sought.
Results Twenty nine patients (19 females, mean age 64 years) were included in the study. Of these in 11 a clinical diagnosis of associated airway reflux was made. The mean [SD] LLMI in the group with airway reflux (95) was not significantly different from those without airway reflux (90). There was a weak correlation observed between the HARQ score and the LLMI (0.09) which was not statistically significant (p = 0.69).
Conclusions We fail to demonstrate significant association between LLMI and either a clinical diagnosis of airway reflux or the HARQ score. This could be due to the fact that macrophages scavenge both exogenous and endogenous material. However our study is limited by small numbers and disparate underlying clinical diagnoses. The small correlation of LLMI with HARQ scores merits further evaluation. Whether the proportion of macrophages phagocytising lipids or the degree of lipid ingestion by the macrophages is more important needs further study.
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