Study design and participants
A cross -sectional study  was conducted at the Pediatric Clinic of Amirkabir Hospital in Arak, Iran, from January 2019 to September 2019. To estimate the sample size, we considered type 1 (α) and type 2 errors (β) of 0.05 and 0.20 (power=80%), respectively, and serum MDA level as a key variable. Based on a previous study12, SD (σ1) of control MDA was 0.1 µmol/L, SD (σ2) of case MDA was 0.07 µmol/L, and the difference in mean (d) of insulin levels was 0.15 µmol/L. We reached the sample size of 9 participants for each group. The sample size of our study consisted of 25 children diagnosed with severe community-acquired pneumonia (sCAP), 25 patients diagnosed with asthma and sCAP, and 25 healthy children.
Pneumonia was defined as an acute pulmonary infiltrate evident on chest radiography with symptoms and signs of a lower respiratory tract infection: fever, cough, and purulent sputum. Pneumonia was confirmed with physical exams, microbiologic culture data, and Chest x-ray. CAP in children was defined as a lower respiratory tract infection in a child who has not resided in a hospital or health care facility in the preceding 14 days. CAP in children is one of the most common acute infections that require going to the hospital. Children with sCAP, due to respiratory distress, are not able to eat, drink, and alert. They also have undesirable hydration status and oxygenation status13-14.
The asthma of children was confirmed by a physician via the symptoms of recurrent coughing, wheezing, and chest tightness.
Exclusion criteria included children with severely smoking parents and severe or multiple systemic diseases.