Red blood cell alloimmunisation after platelet transfusion: a 5-year study.

Abstract

Dear Sir, After platelet transfusion, red blood cell (RBC) antibodies, such as anti-D1, anti-C, anti-E and anti-c2 may develop in the recipient. In France, RBC alloimmunisation detected after transfusion of a blood component is considered as a delayed adverse reaction and is systematically notified to the national haemovigilance database, e-FIT (ANMS - Agence nationale de securite du medicament et des produits de sante, Saint Denis, France). In order to evaluate the incidence of RBC alloimmunisation after transfusion of platelet concentrates, all the adverse reactions reported during a 5-year period were studied. Three parameters were analysed: type of platelet concentrate (PC) involved, specificity of the RBC antibodies, and imputability of the blood component. From January 1st 2007 to 31st December 2011, 3,596 adverse events were reported to the Rhone Alpes e-FIT database. Forty-eight of the adverse reactions (1.3%) were cases of RBC alloimmunisation after platelet transfusion. The number of notified adverse reactions increased during the period studied: 5 cases in 2007 and 2008, 13 in 2009 and 2010, and 12 in 2011. The blood component involved was apheresis PC in 24 cases and pooled PC in 24 cases. The percentage of pooled PC released increased during the 5-year period studied: in 2007, of the total 18,027 PC released, 2,892 (16.0%) were pooled PC, whereas by 2011, the number of PC had risen to 22,753, of which 9,247 (40.6%) were pooled PC (Table I). Of the 48 RBC alloimmunisations notified, 45 had RBC antibodies with only one specificity. Among these, anti-E was the most frequent RBC antibody detected (20 cases, 41.7%), followed by anti-D (15 cases, 31.3%). The other specificities were anti-C (one case), anti-c (two cases), anti-e (one case), anti-cw (one case), anti-D in a D variant (DAU) (one case), anti-K (two cases) and anti-Fya (two cases). Three associations were reported: anti-c and anti-Kpa, anti-c and anti-S, and anti-D and anti-E. Among the alloimmunisation due to anti-D alone, pooled PC were involved in nine cases, and apheresis PC in six. The PC was certainly responsible for the antibody formation in 24 cases (50.0%), probably responsible in 16 cases (33.3%), and possibly in 8 cases (16.7%). Table I Number and type of PLT concentrates released and type of products involved in the post-transfusion RBC alloimmunisations observed during the study. In this study there was a low incidence (1.3%) of RBC alloimmunisation after platelet transfusion and RBC antigens of the Rhesus system were frequently involved. In a study over a 10-year period on D-negative recipients transfused with D-positive PC, Cid et al.3 found 78 cases of RBC alloimmunisation (7.7%) including 49 anti-D (4.8%) and 29 with other specificities (2.9%). Of the 50 patients transfused with pooled PC only, one became alloimmunised, developing antibodies against RBC. The remaining 28 patients, transfused with both apheresis and pooled PC, became alloimmunised against RBC. In practice, several factors are involved in RBC alloimmunisation after platelet transfusion: the volume of residual RBC in the PC, which differs according to studies4. RBC-derived microparticles in the PC may also be involved2; despite the small size of these microparticles, their great number creates a significant volume which may be similar to the volume of the residual RBC themselves. Furthermore, microparticles are probably more immunogenic than RBC as the phagocytosis of these particles by antigen-presenting cells is easier. Finally, the presence of immune depression in the recipient does not protect against RBC alloimmunisation3. In this study performed between 2007 and 2011, reports to the haemovigilance system of RBC alloimmunisation after platelet transfusion increased. Better RBC alloimmunisation screening after platelet transfusion, with detection of new RBC antibodies, partly explains the improvement in notifications to authorities. Close vigilance of RBC alloimmunisation after platelet transfusion must be maintained as the tendency to make increasing use of pooled PC might continue, with a consequent risk of alloimmunisation.