2 | MATERIAL AND METHODS
A prospective study of children aged 1–24 months who were hospitalized with acute bronchiolitis was performed between December 2018 and May 2019. In accordance with American Academy of Pediatrics guidelines, a diagnosis of acute bronchiolitis was based on at least two of the following signs: chest retractions, tachypnea, and the first episode of wheezing or rales on auscultation following a viral upper respiratory tract infection in children aged younger than 24 months6. The study included 179 patients with acute bronchiolitis and 80 healthy children. Inclusion criteria were: aged 1–24 months, first wheezing episode, no previous disease history, and no previous medication. Exclusion criteria were: chronic disease, premature birth, birth weight < 2500 g, malnutrition, passive smoking, proven immune deficiency, proven or suspected acute bacterial infection, previous treatment with bronchodilators or corticosteroids, or having symptoms for more than 7 days. On admission, the clinical severity score (CSS) for acute bronchiolitis (i.e., a composite clinical score including respiratory rate, retraction, wheezing, and general condition) was used to evaluate patients, as previously described by Wang et al .7 Each patient with bronchiolitis was classified into one of three groups, depending on whether they had mild, moderate, or severe bronchiolitis. Complete blood count measurements (including white blood cells, MPV, and platelets) were recorded from the blood samples taken on the first day of hospitalization using a BC-6800 analyzer (Mindray, Shenzhen, China). The IPF was recorded using flow cytometry and the reticulocyte/platelet channel of an XE-5000 automated hematology analyzer (Sysmex, Kobe, Japan) with a fluorescent dye containing polymethrin and oxazine. The IPF is the fraction (%) of immature platelets in the total platelet population. No standard reference range for the IPF has been determined. Data from each patient recorded in the emergency room included: age, sex, disease history, medication, birth history, whether this was the first attack of bronchiolitis, weight, vital signs (i.e., heart rate, respiratory rate, tympanic temperature, and oxygen saturation when breathing ambient air, which was measured using pulse oximetry and expressed as SpO2). The control group included 80 healthy children who attended pediatric clinics for routine health checks or vaccinations. They had similar age/sex demographic characteristics to the children with bronchiolitis. Complete blood counts and IPF data were obtained from blood samples taken for routine testing of these children at their first visit. The families of all children were informed about the study objectives, and written informed consent was obtained before enrollment in the study. The study protocol was approved by the Ethics and Research Committee of Erciyes University (Kayseri, Turkey).