1| INTRODUCTION
Bronchiolitis is the most common lower respiratory tract infection in children younger than 1 year1. Viruses are the most common cause of acute bronchiolitis, especially respiratory syncytial virus. Bronchiolitis is characterized by airway obstruction and edema, increased mucus production, and the loss of airway epithelial cells. The clinical severity of bronchiolitis ranges from mild cases that can be treated on an outpatient basis to severe cases that require mechanical ventilation or extracorporeal membrane oxygenation in intensive care units2. The lack of any single biomarker for acute bronchiolitis that may be applied across all clinical scenarios is a recurring problem and has led many clinicians and researchers to pursue alternative diagnostic strategies.
Platelets play an important role in hemostasis, inflammation, allergic reactions, and angiogenesis, as well as the repair and renewal of tissues. They also secrete mediators such as chemokines, cytokines, and coagulation factors, which provoke a strong inflammatory response and tissue regeneration. Platelet production in bone marrow increases and platelets are redistributed during the inflammatory response3. In addition to platelet count (PLT), platelet indexes include plateletcrit, mean platelet volume (MPV), platelet distribution width (PDW), and a new parameter called the immature platelet fraction (IPF). The IPF is the percentage of reticulated platelets that can be measured in the blood, and it may be used to quantify the production of bone marrow platelets. The IPF correlates directly with the thrombopoietic rate, increasing when platelet production rises and decreasing when production falls. Inflammation causes changes in the bone marrow, leading to increases in platelet production and the circulation of immature platelets4,5. Here, we evaluate the relationship between changes in platelet parameters such as IPF and the clinical severity of acute bronchiolitis.