Cytomegalovirus – It’s a Complicated Topic
Cytomegalovirus, or CMV, is a virus that does not cause any notable symptoms for the majority of general population, or for most patients. About 40 to -50 per cent of adults have been exposed to CMV without any clinical impact. After an exposure, CMV is reported to remain in our white blood cells, and can cause infection if the immune system becomes compromised. CMV can be transmitted by various body fluids, sexual activity, transfusion and transplantation, or from mother to child.
Of particular concern, CMV can cause life-threatening pneumonia in at-risk patients.
The risk of transfusion-transmitted CMV can be reduced by using special filters to remove the majority of white blood cells from cellular blood components. The process is called leukoreduction. Blood components that have been leukoreduced are also referred to as “CMV safe”. Canadian Blood Services implemented universal pre-storage leukoreduction by filtration in June 1999. They also offer “CMV seronegative” blood components made from donors who have tested negative for the CMV antibody to further reduce the risk of CMV transmission by transfusion. There is conflicting literature regarding the benefits of providing leukoreduced blood components as well as CMV seronegative blood components to prevent infection in at-risk patients. For more background, see The Use of CMV Products by Dr. Christine Cserti-Gazdewich.
In an effort to provide clarity for the transfusion community on this topic, the National Advisory Committee on Blood and Blood Products posted a statement on their website (dated August 2014) regarding the appropriateness of use of CMV seronegative versus CMV safe products.
"The National Advisory Committee recommends that CMV safe and CMV IgG seronegative products be considered equivalent for the majority of patient populations including adult and pediatric Hematopoietic stem cell recipients, CMV seronegative patients who may require future transplant and immunodeficient patients. Due to significant controversy and lack of evidence on the need for the provision of CMV seronegative products in addition to leukodepletion in the following patient groups — intrauterine transfusion, neonates under 28 days of age and in elective transfusion of CMV seronegative pregnant women, NAC recommends to follow local policies."
To promote optimal utilization of CMV seronegative platelets, Canadian Blood Services issued a BloodBrief on CMV platelets in March 2015 The data in the BloodBrief highlight the varying demand for CMV seronegative blood components by hospitals in Canada.
Recently, some hospitals have opted to implement policies that do not require CMV seronegative blood components for any of their patients. A list of these hospitals can be found here.
In the absence of definitive data on this topic, hospitals will continue to follow local policies that they feel are most appropriate for their patient population.