4 | DISCUSSION
We found that the IPF, which is a new platelet index, was greater in patients with acute bronchiolitis than in healthy individuals and was positively correlated with the clinical severity of acute bronchiolitis. To our knowledge, this is the first study to investigate the relationship between acute bronchiolitis and IPF. Some cytokines and mediators are activated as part of the response to inflammatory conditions. Inflammation mediates the activation of endotoxins and cytokines, causing immature reticulated platelets (i.e., IPF) to be transferred from the bone marrow to peripheral blood. Platelets stimulate receptors as part of the inflammatory response to pathogens, and interleukins are released to suppress inflammation8–10. Therefore, the IPF is a biochemical and hematological systemic inflammatory marker that can function as an index of platelet activation and production rate in the bone marrow11. Diagnostic accuracy studies performed over the last few years suggest that IPF levels can provide clinically relevant information regarding inflammatory activity and disease prognoses4,11,12. Roberto et al . reported that IPF levels increased in patients with sepsis before sepsis was observed clinically, and they also found that IPF was a better biomarker for sepsis than procalcitonin or C-reactive protein13. Park et al . found that IPF levels were significantly higher in patients with sepsis than in individuals who did not have sepsis5. Rodolfo et al . evaluated the IPF as a biomarker for sepsis diagnosis and severity and found that it was correlated with sepsis severity scores and had the highest diagnostic accuracy for sepsis among all the clinical and laboratory parameters assessed14. Another study found that IPF was strongly positively correlated with MPV and PDW, and attributed this to an increase in the number of larger and wider platelets that appeared after the destruction of pro-inflammatory cytokines and endotoxins as part of a severe inflammatory response15. Together, these findings suggest that IPF levels increase in inflammatory diseases such as sepsis and may be used as an indicator of the inflammatory response. Our observation that the IPF was greater in patients with acute bronchiolitis than in healthy individuals is consistent with previous studies. The clinical severity of acute bronchiolitis was positively correlated with the IPF. Therefore, patients with acute bronchiolitis and high IPF values should be monitored closely after admission to the emergency department. IPF values higher than 3.2% had a specificity of 97% and a sensitivity of 84% for clinical deterioration of acute bronchiolitis.
Platelets play an important role in inflammatory responses, and the PLT increases in many inflammatory diseases. Studies have found that patients with acute bronchiolitis have higher PLTs than healthy individuals16,17. Our patient group had significantly greater PLT values than our healthy control group, and this observation is consistent with previous studies. Our severe bronchiolitis group had higher PLT values compared to our mild bronchiolitis group, but the difference was not statistically significant. During an inflammatory response, depolymerization occurs in the microtubular structure of platelets, and changes also occur in the structure of actin that becomes polymerized; consequently, platelets change their shapes and these changes are reflected in the MPV18. Changes in MPV can be observed before changes in platelet number, so changes in MPV may be useful for predicting inflammation at an early stage and determining its subsequent severity19–21. Among our study population, the MPV was significantly higher in those with moderate and severe bronchiolitis than in those with mild bronchiolitis or in healthy controls, so MPV values may be used to estimate prognoses and the severity of acute bronchiolitis; patients with an MPV value greater than 9 fL should be monitored carefully for clinical deterioration. Several previous studies have evaluated the relationship between acute bronchiolitis and MPV. Gökçe et al .22 found that patients with acute bronchiolitis had higher MPVs than their healthy counterparts, but found no statistically significant differences in MPVs between different bronchiolitis groups. Higher MPVs were observed in children with influenza A respiratory tract infections than in healthy children23. MPVs were also found to be higher in children with pneumonia, asthma, or sepsis than in healthy children24–26. Gasparyan et al .27 found that MPV values were increased in patients with mild inflammation, and they attributed this finding to the transfer of large activated platelets to the site of infection as the severity of inflammation increased. Together, these results suggest that the MPV may also be used to estimate prognoses and the severity of other inflammatory diseases.
PDW, another platelet volume index, shows the variation in platelet diameters and varies by platelet activation. An increase in PDW may occur as a result of swelling, disruption, or platelet immaturity20. In our study, PDW values were significantly greater in patients with moderate and severe bronchiolitis cases than in those with mild bronchiolitis or healthy controls. Ergulet al . found greater PDW values in children with acute bronchiolitis than in healthy children17. PDW may also be greater in patients with sepsis than in healthy individuals, and may be used as a prognostic indicator for patients with sepsis26,28.
The present study had some limitations. It was not a multi-center study. Additionally, we did not characterize the viruses that cause acute bronchiolitis and compare the corresponding clinical severities. The IPF is a novel indicator of inflammation, and it is also a new marker for diagnosing and evaluating the clinical severity of acute bronchiolitis. Larger prospective studies are needed to clarify the clinical significance of using IPF values to assess patients with acute bronchiolitis.
ACKNOWLEDGMENTS
This study received no specific grant from any funding agency in the public, commercial, or not for profit sectors.
CONFLICT OF INTERESTS
The author declares that there are no conflict of interests
AUTHOR CONTRIBUTIONS
Concept and design: MD, MK, MAÖ, MH. Acquisition, analysis, or interpretation of data: MD, HA, MH. Drafting of the manuscript: MAÖ, MK, MD, MH. Critical revision of the manuscript for important intellectual content: MAÖ, MK, HA, MD. Statistical analysis: MD,HA. Administrative, technical, or material support: MAÖ, MK, MD. Supervision: MD, MK, MH.