Hematological profiles of influenza A and B virus infections across different age groups: a retrospective study

Background Neutrophils, lymphocytes, monocytes, the neutrophil-to-lymphocyte ratio (NLR), and the lymphocyte-to-monocyte ratio (LMR) undergo significant alterations during influenza infection. However, cross-sectional comparisons of these parameters across different age groups remain limited for various types of influenza. The objective of this study is to investigate age-related and influenza-specific changes in these hematological indices, as well as to evaluate their predictive value. Methods A retrospective analysis was performed on patients with influenza A and B across different age groups. The study aimed to assess the alterations in routine hematological ratios and to determine their diagnostic and prognostic significance in influenza infection. Results In the B + group aged 4–79 years, the monocyte ratio was significantly elevated, while in the A + group, a significant increase was observed in the 4–59-year age group. The lymphocyte ratio was significantly increased in the B + group aged 40–59 years but markedly decreased in the A + group aged 4–79 years. The neutrophil ratio was significantly elevated in the A + group aged 4–39 years, whereas it was significantly decreased in the B + group aged 20–79 years. The lymphocyte-to-monocyte ratio (LMR) was significantly reduced in the A + group aged 4–79 years and in the B + group aged 4–59 years. The neutrophil-to-lymphocyte ratio (NLR) was significantly elevated in the A + group aged 4–39 years but significantly decreased in the B + group aged 20–79 years. Notably, among the B + group across all age groups, the monocyte ratio demonstrated higher sensitivity and specificity compared with other parameters, whereas in the A + group, LMR exhibited superior sensitivity and specificity across all age groups. Conclusions Routine hematological analysis provides valuable diagnostic insights for both influenza A and B. An increased monocyte ratio may serve as a predictive indicator for influenza B, whereas an elevated lymphocyte-to-monocyte ratio (LMR) may act as a predictive marker for influenza A.