Serum eosinophil cationic protein levels measured during exacerbation of asthma: characteristics of patients with low titres

Background Serum eosinophil cationic protein (ECP) levels reflect ongoing e osinophilic airway inflammation and are used as a marker for asthma activit y. ECP levels, however, may not be elevated in some asthmatic patients, eve n when they are symptomatic. Objective To clarify the characteristics of patients with 'low' ECP titres despite asthma exacerbation. Methods Serum ECP levels were measured in 113 asthmatic patients during exa cerbation. Patients were divided into two groups according to ECP titre: a high ECP group (H; ECP greater than or equal to 16.0 mug/L) and a low ECP g roup (L; ECP < 16.0 mug/L). Twenty-two patients who had recently received s ystemic steroids were excluded and the clinical features of the remaining p atients in H (n = 54) and L (n = 37 were compared. Results Gender, atopic or smoking status, disease severity, inhaled steroid or theophylline usage, peak expiratory flow (% personal best) and forced e xpiratory volume in 1 s (FEV1) (% predicted) did not significantly differ b etween the two groups. Patients in L were significantly older and had longe r disease duration and lower serum IgE levels than those in H. Multivariate analysis combining age, disease duration and IgE levels showed that age an d disease duration were independently associated with ECP level. Airway wal l thickness, assessed in a subset of patients using computed tomography, wa s significantly larger in L. Conclusion Serum ECP levels in asthmatic patients may not be elevated durin g exacerbation and thus may not be a useful marker in patients who are olde r, have longer disease duration or possibly have thicker airway walls. Mech anisms other than eosinophilic inflammation, such as airway remodelling, ma y be involved in asthma exacerbation in these patients.