In response to Joubeh and Singh: Allergic reactions to platelets; to B or not to B?

We read the recent letter by Joubeh and Singh discussing allergic reactions to psoralen-treated platelets (PI-Platelets) and found their data intriguing. These authors describe two cases of O+ male patients developing allergic reactions after psoralen-treated platelet transfusions, and they wonder whether PI-Platelets may cause allergic transfusion reactions. However, as they noted, the allergic reactions in these patients were exclusively to AB or B platelets, raising the possibility that the ABO compatibility may provide a better explanation for their results than the PI-Platelets. In fact, we recently examined transfusion reaction rates in platelets and found that A or B antigen incompatible platelets (analyzed in aggregate) had higher rates of allergic reactions compared to ABO compatible transfusions. To examine specifically whether Type B platelets may cause allergic reactions in some patients, platelet transfusion records from October 2015 to April 2022 were analyzed. As previously described, these records were merged with patient and product ABO type as well as with a transfusion reaction data set that included all reported reactions to platelet transfusions during that time. Allergic reaction rates for type O patients to O, A, B, and AB were calculated and demonstrated that AB/B platelets were significantly more likely to cause allergic reaction in type O patients than O or A platelets (Table 1). Analysis of these data using the Fisher's Exact test showed that these differences were highly significant (OR = 2.53, p = 0.0072). Reaction rate in type A patients found the allergic reaction rate for AB/B platelets was 0.41% which was not significantly (p = 0.59) different than the rate for A/O platelets (0.31%). The data were also analyzed to determine if allergic reaction rates for psoralen-treated (PT) platelets were higher than the rate found for non-psoralen-treated platelets. The rate of allergic reaction to PT platelets was (1 in 214 PT and 0 of 177 PT-PAS0.26% overall) not statistically different (p > 0.99) than for conventional platelets (112 in 31,645–0.36%) (p > 0.99). While likely under-powered, this does not support the possibility that psoralen treated platelets increase allergic reaction rates as suggested previously. In our data set there were 10 type O patients and 4 type A patients who had allergic reactions to B or AB platelets. A summary of the platelet transfusions and allergic reactions for these 14 patients is shown in Table 2. Of these patients, two were particularly noteworthy, as they received more than 20 transfusions and allergic reactions were noted only when B platelets were transfused. Patient 1 was a male in his 70s who received 22 transfusions and he had three allergic reactions to all three B platelets (7th, 13, and 16th transfusion) he received. Patient 2, also a male in his 70s, received 23 transfusions and had allergic reactions to both B platelets he received (1st and 8th transfusion). Of note, neither patient 1 or 2 was noted to have environmental allergies. Five other Type O patients (Table 2 #3–7) were found that had allergic reactions to all B antigen positive units they received but these patients received fewer platelet transfusions, and all had just a single allergic reaction making the possibility that this occurred by chance much higher. Two of these patients had a reaction on the first platelet transfusion they received. Of the four type A patients, only one (#11) had a reaction to all the B antigen positive platelets they received but this patient only received three platelet transfusions in total, so it is unknown if this is related to the B antigen. It is noteworthy that 11 of the 14 patients described here (included patient 1 and 2) and both of the subjects described by Joubeh et al.were male. It is unclear if this occurred by chance or not. In our view, these data coupled with the previous report by Joubeh et al. can best be explained by a small fraction of patients who have allergic reactions to the B antigen expressed on platelets or secreted in plasma. In our study, there were 890 type O patients transfused with 1798 units of B or AB products and an allergic reaction was reported in only 10 (1.1%) of these patients. We estimate that this is the upper limit for allergic reaction to the B antigen as it is very unlikely that all of these were due to the B antigen.