Eosinophil cationic protein in sputum is dependent on temperature and time

Eosinophil cationic protein (ECP) in sputum may be used to estimate the severity of bronchial inflammation and obstruction in asthmatics as well as to monitor asthma drug therapy. For this purpose, standardized processing of sputum is important. The aim of our study was to determine whether time and temperature influence the ECP concentration in the sputum of asthmatics. The samples of induced sputum obtained from 12 patients with stable asthma were homogenized using ultrasonification, and centrifuged. Supernatants were evenly divided and stored for 1, 6, 24 or 72 h at either 4 or 25 degrees C, then frozen at -80 degrees C. The ECP concentrations were determined using fluoroimmunoassay and compared with the immediately frozen samples. After storing at 4 degrees C, the ECP levels at the four time points were 101.2, 96.0, 98.2 and 90.6% of the initial concentration, respectively. When sputum specimens were stored at 25 degrees C, ECP levels decreased to 96.1, 94.4, 90.7 and 87.7%, respectively. The influence of time on ECP concentrations in sputa was statistically significant (p=0.02). A significant temperature effect was found when comparing the specimens stored at 4 degrees C with those at 25 degrees C (p=0.03). Looking at individual time points, a significant decrease in ECP concentration was only seen at 25 degrees C after 24 and 72 h. We conclude that eosinophilic cationic protein in the sputum of asthmatics decreases in a time- and temperature-dependent process. If sputa cannot be processed after obtaining the specimens, they should be stored in a refrigerator at 4 degrees C, until eosinophilic cationic protein is measured.