Serologic assessments in acute transfusion reactions: practices and yields

Background & objectives: Serologic testing after transfusion reactions (TRs) aims to find accountable immune haemolytic incompatibility. Our hospital policies recommend serologic testing in all TR, except for low-risk fevers (subclinical temperature <39°C) or uncomplicated allergic reactions. Assessing compliance with these guidelines and serologic testing yields may provide insights on quality of practice and value.

Materials & methods: Interrogation of two haemovigilance databases identified all possible-to-definite TR over a 4-year period (2013-2016) at four academic hospitals. We reviewed the performance and outcome of serologic testing by site, year, reaction type, implicated product and service.

Results: Serologic testing occurred in 769 (55%) of 1408 referrals, with 1153 (82%) compliant with guidelines. Similar proportions deviated to overtesting (85/550 [15%]) and undertesting (174/858 [20%]), with undertesting seen most often in atypical TR. Overall, 30 (4.4%) of 769 cases had a new finding, but only 2 (0.3%) reflected host-derived antibodies. Overall, the number needed to test to discover an unexpected allospecificity was 385, or 253 if limited to high-risk fevers. Reaction- and product-specific yields ranged from 0% to 48%. The yield in complicated allergic reactions was low at 2%, constituting only predictable passive isohaemagglutinin(s) in retrospect. Investigated IVIG TR accounted for most of this cohort's signal by passive isohaemagglutinins in 48%.

Conclusion: The performance of post-TR serologic testing revealed practice gaps and expected context-specific yields. Tailored serologic testing (i.e. indirect antiglobulin tests for alloantibodies in post-RBC/high-risk febrile reactions, ± isoagglutinin-focused tests after IVIG or ABO-minor-mismatched platelets) may improve value and liberate resources for other unmet needs in TR investigation.