CMV Safe Blood Components
Cytomegalovirus (CMV) is a DNA virus of the herpesvirus family. Transfusion acquired CMV is of little concern in immunocompetent individuals, but can be a serious problem in immunocompromised patients. In the latter group of patients, CMV transmission can result in pneumonitis, hepatitis, gastroenteritis, chorioretinitis, or disseminated disease. CMV negative blood components are indicated for fetal and intrauterine transfusions, low birth weight premature infants born to CMV seronegative mothers and CMV negative recipients of organ, peripheral blood stem cell or bone marrow transplants from CMV negative donors.
Between 50 and 80% of the US population has been infected with CMV. Traditionally, blood banks test donors for antibodies to CMV to try to prevent viral transmission to immunocompromised patients. Labelling a unit as seronegative indicates that the unit does not contain detectable antibodies against CMV, but does not mean the unit cannot transmit CMV. A donor with a recent infection can harbor virus in their plasma or white blood cells even though they test negative for antibodies. The window period for CMV infection is estimated to be 6 to 8 weeks. As with all laboratory tests, there is the possibility of a false-negative antibody test in an infected donor.
In established infections, CMV resides in a small minority of monocytes. This means that risk of CMV transmission can be greatly diminished by leukocyte reduction of donor units, which removes at least 99.9% of leukocytes. Studies have estimated that fewer than 25 potentially infected monocytes remain following leukocyte reduction by either filtration or apheresis. During the viremic phase of an acute infection, some virus may circulate in the plasma and not be removed by leukocyte reduction. Neither antibody testing or leukocyte reduction will prevent transmission of CMV in this scenario.
In 1995, the Bowden study compared CMV transmission rates in bone marrow transplant recipients receiving either CMV seronegative or filtered blood products (Blood, Vol 86, No 9, 1995: pp 3598-3603). This study did not detect any significant difference in CMV transmission between either group.
Since 1997, AABB has considered leukocyte reduced blood to be a CMV safe product that is equivalent to CMV seronegative units for preventing CMV transmission. The Circular of Information for the Use of Human Blood and Blood Components (prepared jointly by AABB, American Red Cross, America’s Blood Centers and Armed Services Blood Program and recognized by FDA) lists leukocyte reduction as an alternative to CMV seronegative products.
Filtration technology for leukocyte reduction has greatly improved since publication of the original study. Today all red cell units are leukocyte reduced by filtration and platelets are leukocyte reduced by apheresis. Many transfusion services consider leukocyte reduced products to be CMV safe and automatically substitute them for CMV negative orders in adult patients.
