In this research study we want to learn more about the character of neutrophils that are present in the blood of children with sepsis. Sepsis is a severe type of infection, affecting various parts of the body. Neutrophils are a type of white blood cell that are part of the body's immune system. Even though neutrophils are important in getting rid of germs, they also may be harmful to parts of the body by causing injury in organs in patients with sepsis. Neutrophils can change their character in sepsis. Because of this, it is important for doctors to know what kind of neutrophils are in the blood of children with sepsis so that they can work to develop therapies to prevent these cells from being harmful.

Inclusion criteria Patients will be eligible for enrollment as septic patients if they

• Are < 18 years old
• Meet the definition of sepsis described in the study design section above. Patients will be eligible for enrollment as control patients if they
• Are < 18 years old
• Are scheduled for an elective surgical procedure and need preoperative blood draw or will have an intravenous catheter placed for the purpose of their surgical procedure.

Exclusion criteria Patients will be ineligible for enrollment in either control or sepsis group if any of the followings is present or anticipated

• Congenital cardiac disease
• On chronic immunosuppressive drugs such as chronic corticosteroid use, or preexisting immunodeficiency diseases

We will enroll pediatric patients with sepsis in an ICU at Boston Children's Hospital and patients without sepsis presenting for an elective surgical procedure at Boston Children's Hospital.