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Donor MBL, CLL status does not raise risk for CLL following transfusion
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Recipients of blood transfusions from donors later diagnosed with chronic lymphocytic leukemia did not face an increased risk for contracting the disease themselves, according to the results of an observational study.
Monoclonal B-cell lymphocytosis (MBL) — or the presence of small monoclonal B-cell subpopulations in the peripheral blood of healthy individuals — acts as a precursor of CLL. Although MBL occurs somewhat frequently in healthy individuals, the incidence of MBL in blood donors has raised concern that transmitted MBL may cause CLL in the recipient of the blood transfusion, according to the researchers.
Henrik Hjalgrim, MD, PhD, an epidemiologist at Statens Serum Institut in Copenhagen, and colleagues conducted an observational study to determine whether MBL elevated the risk for CLL in patients receiving blood transfusions. They accessed the Scandinavian Donations and Transfusions database, which includes data on vital status and health outcomes for patients treated in Sweden and Denmark.
The researchers collected health information from 1.5 million donors and 2.1 million transfusion recipients. They compared data from 7,413 transfusion recipients from 796 donors who later received a diagnosis of CLL (exposed group) with data from 80,431 recipients from 7,477 matched donors without CLL (unexposed group).
During follow-up, 12 patients from the exposed group and 107 patients from the unexposed group received a CLL diagnosis (RR = 0.94; 95% CI, 0.52-1.71).
Analyses using the entire database did not show evidence of CLL clustering among recipients of blood from individual donors.
The researchers acknowledged limitations of their study, including their lack of data on MBL status from actual donors. Further, they noted that until recently, Scandinavians aged 65 years or older received deferment from blood donation, and because MBL and CLL incidence increases with age, the researchers acknowledged that blood products from older donors may increase CLL risk.
“Resting on the entire computerized transfusion experience in two countries during more than 30 years, our analyses provide no evidence that donor MBL/CLL transmission contributes significantly to CLL risk among transfusion recipients,” Hjalgrim and colleagues wrote. – by Cameron Kelsall
Disclosure: The researchers report no relevant financial disclosures.
Perspective
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Kanti R. Rai, MD
The work presented by Hjalgrim and colleagues is important on two grounds. First, from prior reports, there might be concern that up to 3.5% of the general population harbors very small numbers of lymphocytes in their blood, which — by phenotyping (flow cytometry) — are nondistinguishable from lymphocytes of patients with chronic lymphocytic leukemia. This phenomenon has been studied extensively in the last decade. Now, it has been named monoclonal B lymphocytosis (MBL). Individuals with MBL otherwise look normal and act normal, but a very small proportion of them do develop real CLL. It is believed that virtually every person who is diagnosed with CLL has previously gone through a phase of MBL, but not every person with MBL develops CLL.MBL is a condition that remains silent, and the person with it is in all other respects entirely normal. Thus, our healthy blood donor pool might have people with MBL. The concern is that if we transfuse to a needy patient blood from a donor who has MBL, are we putting the recipient at risk for developing MBL or CLL? This well-planned, thorough and elegantly conducted study lays to rest this concern. Hjalgrim and colleagues have done a great service and have convincingly presented their results.
The other aspect of this study that deserves a mention — and perhaps some further discussion among hematologists/oncologists — is that in Sweden and Denmark, people were deferred from donating blood after they reached age 65, but that is a restriction no more. The age limit has been abolished. In my opinion, this is welcome news. As our population ages and many of our elderly continue to remain active and maintain good health, it is important that we as a society do everything to maintain and even expand our blood donor pool. Thus, this report brings us good and reassuring news on two fronts.
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