A separate study (similar subjects) identified transfusion-associated microchimerism only rarely, making this observational study impractical to conduct.

Blood transfusions are frequently necessary in situations in which there is a large amount of blood loss. In some individuals who receive a blood transfusion, white blood cells from the donor's blood may remain in the body for years, a condition known as microchimerism. This study will evaluate the occurrence of microchimerism among the following three groups of individuals who previously received transfusions: 1) individuals with traumatic injuries; 2) individuals with burn injuries; and 3) individuals who underwent elective orthopedic operations.

Approximately 10% to 15% of injured patients who receive blood transfusions experience a condition known as transfusion-associated microchimerism. This occurs when white blood cells, or leukocytes, from the donor's blood persist in the recipient long after the transfusion occurs. The genetically distinct donor cells can remain in the individual for decades, and may account for as many as 4% of the white blood cells in the recipient's body. This suggests that the donor cells are tolerated by the recipient's immune system. The purpose of this study is to compare the incidence of microchimerism among individuals with three different types of injuries: 1) traumatic injuries; 2) thermal, or burn, injuries; and 3) injuries resulting from elective orthopedic surgical procedures.

In this study, blood samples will be collected from individuals who were treated for traumatic injury, thermal injury, or elective orthopedic surgical procedures at the University of California at Davis Medical Center. Individuals who were treated from 2000 to 2003 and received a blood transfusion, as well as a control group of individuals who did not receive a transfusion, will be approached to enroll in the study. Individuals who agree to participate will have their blood analyzed for evidence of microchimerism. Information on health status, injury characteristics, hospital care, blood transfusion details, and blood donor characteristics will be collected from all participants.

Inclusion Criteria:

• Hospitalized for traumatic injury, thermal injury, or an elective orthopedic surgical procedure from 2000 to 2003 at the University of California at Davis Medical Center
• Received at least 1 unit of transfused red blood cells

Exclusion Criteria:

• Currently incarcerated
• Inadequate decision-making capacity of the participant and no available surrogate decision-maker
• Prior bone marrow or solid organ transplantation
• Prior blood transfusion other than at the time of hospitalization
• Any history of an autoimmune disorder prior to hospitalization

Previously hospitalized patients