Limitations and strengths
There are several limitations in the present study. First, the diagnostic performance of serum periostin in identifying children with severe asthma were relatively low. It seems that further studies including more children particularly with severe asthma can help to determine different cut-off values with better statistical performances. Furthermore, periostin is a bone-derived extracellular matrix protein that is secreted by osteoblasts and in growing children the indicative role of periostin related to the airway inflammation and consequently asthma severity may be affected due to the fast-linear growth in school-age children. On the other hand, it was performed in a center which was specialized for children with asthma and allergic diseases. The diagnostic procedures and the longitudinal follow-up of the patients were made by pediatric allergy and asthma specialists conforming with the international standard GINA guidelines. Its controlled design with the inclusion of patients with different severity grades who were under regular follow-up enabled us to demonstrate the possible interactions between features related to childhood asthma and periostin.