Is serum or sputum eosinophil cationic protein level adequate for diagnosis of mild asthma?

Spirometry has been used as a common diagnostic test in asthma. Most of the patients with a mild asthma have a FEV1 within normal range. Hence, other diagnostic methods are usually used. The aim of this study was to evaluate whether eosinophil Cationic Protein (ECP) could be an accurate diagnostic marker of mild asthma. In this study diagnosis of asthma was made according to internationally accepted criteria. Asthma severity was evaluated according to frequency of symptoms and FEV1.Adequate sputum samples were obtained in 50 untreated subjects. A control group of 12 normal subjects that showed PC20 more than 8 mg/dl was also examined. Sputum was induced by inhalation of hypertonic saline. Inflammatory cells in sputum smears were assessed semi-quantitatively. ECP and IgE concentrations, eosinophil (EO) percentage and ECP/EO ratio in serum and sputum were also determined. The results revealed that Cough and dyspnea were the most frequent clinical findings. Dyspnea and wheezing were the symptoms that correlated with staging of asthma. FEV1 was within normal range (more than 80% of predicted) in 22 (44%) subjects.Asthmatic patients showed significantly higher numbers of blood eosinophils (4.5+/- 3.1% vs. 1.2+/-0.2%, P=0.009), and higher levels of serum ECP than control group (3.1+/- 2.6 % and 22.6+/- 15.8 ng/ml, respectively). Sputum ECP level in asthmatics was significantly higher than non- asthmatics (55.3+/-29.8ng/mL vs. 25.0+/-24.7ng/mL, P=0.045). Regression analysis showed no significant correlation between spirometric parameters and biomarkers, the only exception was significant correlation between FEF(25-75) and serum ECP (r= 0.28, P 0.041). Regarding clinical symptoms, wheezing was significantly correlated with elevation of most of biomarkers. Since, serum and sputum ECP levels are elevated in untreated asthmatics, the ECP level could be used for accurate diagnosis of mild form of asthma in which spirometry is unremarkable.