The main function of hemoglobin is to transport oxygen and carbon dioxide, and the level of hemoglobin is closely related to the adverse outcomes of infected patients. Low hemoglobin level may indicate higher infection incidence, disease severity and mortality. As a simple, rapid, and economical clinical indicator, hemoglobin may become a biomarker for predicting adverse outcomes in infected patients. This paper reviews the relationship between hemoglobin levels and adverse outcomes as well as the predictive value in infected patients, with the aim of helping clinicians (especially those in outpatient departments and primary hospitals) to understand the clinical signi-ficance of monitoring hemoglobin levels, so as to accurately identify high-risk infected patients, optimize treatment and referral decisions.