To evaluate the prognostic role of initial band percentages in adults presenting to the emergency department (ED) with bacteremia.

This 8-year retrospective cohort study included treatment-naïve adults with bacteremia who underwent a manual differential hemogram. The primary outcome was 30-day mortality after ED arrival. The association between initial band percentages and mortality was analyzed using a logistic regression model adjusted for independent prognostic factors.

Of the total 5558 patients, patients were stratified into five groups by the initial percentage of band cells (neutrophils): 0%–10% (3358 patients), 10%–19% (849), 20%–29% (618), 30%–39% (347), and ≥ 40% (386). The groups varied significantly in terms of clinicodemographic characteristics, bacteremia profiles, and mortality rates at 3, 15, and 30 days. Overall, each 10% increase in the initial band percentage was independently associated with an average 12% increase in 30-day mortality rates. The positive association between initial band percentages and 30-day mortality rates remained consistent across predefined patient subgroups.

A higher initial percentage of band cells is independently associated with a higher risk of short-term mortality in adults presenting to the ED with bacteremia.