Diagnostic accuracy of sputum outcomes in chronic stable asthma

Background Asthma with non-remitting airflow obstruction may not always be differentiated from COPD with airway hyperreactivity. Many attempts have be en made to find useful markers for the distinction between these two disord ers. Objective and methods In order to help the finding of a useful marker for t he diagnosis of asthma in the population of patients with airway obstructio n we analysed the diagnostic accuracy of sputum eosinophils and sputum ECP in 91 patients with asthma, 15 patients with chronic bronchitis, 32 patient s with chronic obstructive pulmonary disease (COPD) and 20 controls subject s, by performing ROC analysis. Results Sputum eosinophils were above the normal range of our laboratory (0 -3.7%) in 48 asthma patients and in six COPD patients, while sputum ECP (no rmal range < 85 mu g/L) was high in 65 asthma patients, in 24 COPD patients and in nine chronic bronchitis patients. The ROC analysis revealed that sp utum eosinophils count (AUC = 0.82) was more accurate than both sputum ECP levels (AUC = 0.56) (P < 0.0001) and beta(2)-reversibility (AUC = 0.53) (P = 0.0001) in differentiating asthmatic from non-asthmatic subjects (COPD, c hronic bronchitis patients and normal subjects). The diagnostic accuracy of ECP was similar to that of bronchial reversibility (P = 0.76). When ROC an alysis was performed by including only patients with airway obstruction (36 asthmatics with airway obstruction and COPD patients), both eosinophil cou nt (AUC = 0.77) and beta(2)-reversibility (AUC = 0.66) were more accurate t han ECP measurement (AUC = 0.39) in discriminating asthmatics from COPD pat ients (P < 0.00001 and P = 0.04, respectively). Conclusion Sputum eosinophils seem to be valid markers for detecting asthma in a population of patients with airway obstruction. Moreover, the higher diagnostic accuracy of eosinophils in the sputum compared to sputum ECP and bronchial reversibility reinforces the role of cytological analysis of spu tum in the diagnosis of chronic stable bronchial asthma.