OBJECTIVES: To determine the reliability of the Bleeding Assessment Scale in critically Ill Children (BASIC) definition of bleeding severity in a diverse cohort of critically ill children. DESIGN: Prospective cohort study. SETTING: Eight mixed PICUs in the Netherlands, Israel, and the United States. SUBJECTS: Children ages 0-18 years admitted to participating PICUs from January 1, 2020, to December 31, 2022, with bleeding noted by bedside nurse. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The bleeding events were classified as minimal, moderate, or severe, according to the BASIC definition, by two independent physicians at two different time points. Patient demographic data, laboratory values, and clinical outcomes were collected. Three hundred twenty-eight patients were enrolled. The overall inter-rater reliability was substantial (weighted kappa coefficient, 0.736
95% CI, 0.683-0.789), and the intra-rater reliability was "almost-perfect" (weighted kappa coefficient, 0.816
95% CI, 0.769-0.863). The platelet count ( p = 0.008), prothrombin time ( p = 0.004), activated partial thromboplastin time ( p = 0.025), and fibrinogen levels ( p = 0.035) were associated with the bleeding severity, but the international normalized ratio was not ( p = 0.195). Patients were transfused blood components in response to any bleeding in 31% of cases and received hemostatic medications in 9% of cases. More severe bleeding was associated with increased 28-day mortality, longer hospital length of stay, and more days receiving inotropic support. CONCLUSIONS: The BASIC definition is a reliable tool for identifying and classifying bleeding in critically ill children. Implementing this definition into clinical and research practice may provide a consistent and reliable evaluation of bleeding.