Immature Platelet Fraction as a Marker of Influenza-Associated Co-Infection in Emergency Department Patients

BackgroundInfluenza is a major respiratory pathogen worldwide, and bacterial co-infection substantially contributes to adverse outcomes. However, early recognition of co-infection in the emergency department remains challenging. The immature platelet fraction (IPF) has demonstrated diagnostic value in sepsis, whereas its role in viral infections and bacterial co-infection is unclear. This study aimed to evaluate whether IPF can serve as a marker for identifying influenza patients with co-infection.MethodsWe retrospectively identified adult patients presenting to the emergency department of National Taiwan University Hospital between May 2023 and December 2024 who underwent influenza testing and complete blood count with IPF measurement. Patients were categorized as influenza mono-infection, influenza with co-infection, or non-influenza. Laboratory parameters, including IPF and white blood cell (WBC) counts, were compared, and risk factors associated with co-infection among influenza patients were evaluated.ResultsA total of 365 patients were included, of whom 134 (36.7%) tested positive for influenza. IPF tended to be lower in influenza-positive than influenza-negative patients (5.7% vs. 6.1%, p = 0.054). Among influenza-positive patients, 41 (30.6%) had co-infection. IPF was higher in patients with co-infection than in those with influenza mono-infection (6.5% vs. 5.1%, p < 0.05). The combined criterion of WBC ≥ 10×10⁹/L and IPF ≥ 6% was independently associated with co-infection (adjusted OR, 9.91; 95% confidence interval: 2.80-35.10; p < 0.01).ConclusionsHigher IPF is associated with co-infection among patients with influenza. When combined with WBC, IPF may serve as a useful marker for identifying co-infection at emergency department presentation.