Accuracy of Alpha Amylase in Diagnosing Microaspiration in Intubated Critically-Ill Patients

Objectives: Amylase concentration in respiratory secretions was reported to be a potentially useful marker for aspiration and pneumonia. The aim of this study was to determine accuracy of alpha-amylase in diagnosing microaspiration in critically ill patients. Methods: Retrospective analysis of prospectively collected data collected in a medical ICU. All patients requiring mechanical ventilation for at least 48 h, and included in a previous randomized controlled trial were eligible for this study, provided that at least one tracheal aspirate was available for alpha-amylase measurement. As part of the initial trial, pepsin was quantitatively measured in all tracheal aspirates during a 48-h period. All tracheal aspirates were frozen, allowing subsequent measurement of alpha-amylase for the purpose of the current study. Microaspiration was defined as the presence of at least one positive tracheal aspirate for pepsin (>200 ng.mL(-1)). Abundant microaspiration was defined as the presence of pepsin at significant level in >74% of tracheal aspirates. Results: Amylase was measured in 1055 tracheal aspirates, collected from 109 patients. Using mean alpha-amylase level per patient, accuracy of alpha-amylase in diagnosing microaspiration was moderate (area under the receiver operator curve 0.72 +/- 0.05 [95% CI 0.61-0.83], for an alpha-amylase value of 1685 UI.L-1). However, when alpha-amylase levels, coming from all samples, were taken into account, area under the receiver operator curve was 0.56 +/- 0.05 [0.53-0.60]. Mean alpha-amylase level, and percentage of tracheal aspirates positive for alpha-amylase were significantly higher in patients with microaspiration, and in patients with abundant microaspiration compared with those with no microaspiration; and similar in patients with microaspiration compared with those with abundant microaspiration. alpha-amylase and pepsin were significantly correlated (r(2) = 0.305, p = 0.001). Conclusion: Accuracy of mean alpha-amylase in diagnosing microaspiration is moderate. Further, when all alpha-amylase levels were taken into account, alpha-amylase was inaccurate in diagnosing microaspiration, compared with pepsin.