As an adult Infectious Disease physician many of the calls I receive stem from concerning labs. The most common calls are concern for sepsis in a patient with leukocytosis and “bandemia”. Leukocytosis while a reliable marker of bacteremia in the pediatric population is woefully non-specific for sepsis in adults with AUC ROC of about .500. Similarly, the presence of immature band forms in not predictive of sepsis or bacteremia. It turns out that much more can be cleaned about the likelihood of sepsis and bacteremia from other components of the WBC differential. A neutrophil to lymphocyte count ratio greater than 10 has been demonstrated in numerous studies to be almost as good as serum Procalcitonin at predicting bacteremia. Additionally an absolute lymphocyte count < 1000 is highly predictive of bacteremia. While physicians tend to notice eosinophilia as a marker of allergic reactions or fungal infection, eosinopenia with an absolute eosinophil count < 40 cells/ microliter r...