Serum amyloid A (SAA) in induced sputum of asthmatics: a new look to an old marker.

Background: Some cellular and soluble markers of inflammation in induced sputum have been used for studying airway inflammation in asthma. The aim of this study was to assess the usefulness of systemic inflammation marker serum amyloid A (SAA) in blood and induced sputum to monitor the airway inflammation in asthmatic patients.

Method: Seventeen non-smokers newly diagnosed mild to moderate asthmatic patients and 10 healthy volunteers were included in this prospective parallel designed study. Inflammatory cell counts, SAA and eosinophil cationic protein (ECP) levels were measured in sera and induced sputum of both groups. All tests were repeated in the asthma group after 6 months of inhaled steroid therapy. The diagnostic accuracy and reproducibility of sputum and blood SAA were estimated.

Results: Serum and induced sputum SAA and ECP levels, sputum eosinophils and neutrophils of untreated asthmatic patients were significantly greater compared to the control group. Sputum and sera SAA levels and sputum neutrophils remained unchanged after the 6 months of anti-inflammatory therapy, although ECP levels, sputum eosinophils and macrophages were significantly reduced. The area under the curve (AUC) for sputum SAA was found equal to AUC for sputum ECP (0.87). The reproducibility of sputum SAA was satisfactory (ICC=0.84) as well.

Conclusion: Our findings suggest that systemic inflammatory marker SAA may be used as a reliable inflammatory marker in asthma. The facts that whether it remarks an ongoing inflammation unresponsive to treatment in the airways or reflects a systemic inflammation needs to be clarified with further studies.