The persistence of red cell alloantibodies.

Background: Red cell alloantibodies may disappear over time and cause a delayed haemolytic reaction if their past existence is not known before a transfusion. Only few quantitative data have already been presented on this topic.

Study Design And Methods: We retrieved the records of alloantibodies detected between 1989 and 2008 in our institution. All warm-reacting alloantibodies were included, with the exception of ABO antibodies, anti-D in women of childbearing age (it was impossible to rule out Rh prophylaxis) and antibodies produced by transfusion-dependent beta-thalassaemia patients (their transfusion history was too unusual).

Results: We found 673 antibodies, produced by 525 patients, which had been tested again after the initial detection. The median follow-up was 319 days. The overall rate of non-persistence was 37%, corresponding to 251 antibodies, produced by 216 patients. Non-persistent antibodies were associated with a longer follow-up (409 vs. 236 days; p=0.012), more tests after detection (2 vs. 1; p<0.001), and a lower maximum score (2+ vs. 3+; p<0.001). Antibody specificity, too, influenced the duration of persistence. Among common antibodies, anti-D was the most long-lived (14% non-persistence); anti-Jka the most short-lived (43% non-persistence). Antibodies detected in the second decade of the study were less persistent (p<0.001). They were also weaker (maximum score: 2+ vs. 3+; p<0.001). This probably reflects the increased sensitivity of the screening tests over the course of time. Age, sex and whether the patient had produced multiple alloantibodies were not significant covariates. A minority of non-persistent antibodies (33/251, 13%) were detected again after a negative result (intermittently-detected antibodies). They had a longer follow-up (885 vs. 341 days; p=0.002), more tests after detection (5 vs. 2; p<0.001), and a higher maximum score (3+ vs. 2+; p=0.001).

Conclusions: Red cell antibodies commonly disappear. To avoid delayed haemolytic reactions, it is necessary to rely on previous records, which should be readily available.