Analysis of data from blood transfusions that took place in Sweden and Denmark over a 30-year period showed no indication that chronic lymphocytic leukemia (CLL) risk is higher among recipients of blood from donors who subsequently developed CLL, according to researchers.

The study compared 7,413 recipients of blood from 796 donors who subsequently developed CLL (exposed group), with 80,431 recipients from 7,477 donors free of CLL (unexposed group). In total, 12 recipients in the exposed group and 107 in the unexposed group were later diagnosed with CLL, for an incidence rate ratio of 0.94 (95% confidence interval, 0.52-1.71). When defining “exposed” as receiving blood less than 10 years before donor CLL diagnosis, the incidence rate ratio was 0.46 (95% CI, 0.12-1.85).

“The analyses provided little evidence that donor MBL [monoclonal B-cell lymphocytosis]/CLL transmission in blood products influences recipient CLL risk,” wrote Dr. Henrik Hjalgrim of the department of epidemiology research at Statens Serum Institut, Copenhagen, and his colleagues (Blood 2015 doi: 10.1182/blood-2015-03-632844).

MBL is fairly common in healthy individuals (estimated at 7.1% in a study of American blood donors aged 45-91 years) and may progress to CLL at various rates depending on the MBL cell count. Results from previous studies investigating the association between transfusion and risk of CLL or small lymphocytic lymphoma have been mixed, they noted.

Using a retrospective approach, Dr. Hjalgrim and his associates first identified donors subsequently diagnosed with CLL, then identified control donors free from CLL who were matched for age, sex, county, number of donations, and blood type.

In case MBL may have progressed in the recipient but not the donor, investigators also examined whether CLL clustered among recipients from an individual donor, regardless of donor CLL status, but found no such clusters.

Limiting the analysis was the lack of donor MBL status, for which postdonation CLL diagnosis substituted. Some recipients in the exposed group may have received blood drawn before the donor developed MBL.

Dr. Hjalgrim and his coauthors reported having no disclosures.