Systemic immune-inflammation index in predicting hospitalized bronchiectasis exacerbation risks and disease severity

Bronchiectasis is a common respiratory disease with neutrophilic inflammation being the predominant pathophysiology. Systemic immune-inflammation index (SII) is a simple and readily available biomarker being studied in various conditions including asthma, chronic obstructive pulmonary disease, and interstitial lung disease, but not in bronchiectasis. We aim to investigate the prognostic role of SII in bronchiectasis with this study.

A retrospective cohort study in Chinese patients with non-cystic fibrosis (CF) bronchiectasis was conducted in Hong Kong, to investigate the association between baseline SII and of hospitalized bronchiectasis exacerbation risk over 4.5 years of follow-up, as well as correlating with disease severity in bronchiectasis. The baseline SII in 2018 was calculated based on stable-state complete blood count.

Among 473 Chinese patients with non-CF bronchiectasis were recruited, 94 of the patients had hospitalized bronchiectasis exacerbation during the follow-up period. Higher SII was associated with increased hospitalized bronchiectasis exacerbation risks with adjusted odds ratio (aOR) of 1.001 [95% confidence interval (CI): 1.000-1.001, P=0.003] for 1 unit (cells/µL) increase in SII count and aOR of 1.403 (95% CI: 1.126-1.748, P=0.003) for 1 standard deviation (SD) increase in SII. SII was found to have significant negative association with baseline forced expiratory volume in the first second (FEV₁) (in litre and percentage predicted), forced vital capacity (FVC) in percentage; and significant positive correlation with the extent of bronchiectasis and baseline neutrophil to lymphocyte ratio (NLR).

SII could serve as biomarker to predict the risks of hospitalized exacerbation in bronchiectasis patients, as well as correlating with the disease severity.