Raised immunoglobulin E levels are not predictive of allergic reactions to blood products.

Sir,

The report by Shanthi et al. on an acute allergic reaction after platelet transfusion in the patient with cerebral malaria needs clarification on a few points.[1] The authors suggest that this was an immunoglobulin G and E (IgG and IgE)-mediated reaction although the reasons behind this conclusion were not justified. The gel column tube merely shows an indirect antibody test against complement coated red cells, and not a specially designed column to detect IgG against platelets. Secondly, raised IgE levels after transfusion does not indicate an IgE-mediated event and the authors have not provided the IgE levels before the transfusion. The authors acknowledge that IgE levels are known to be raised in cerebral malaria, but continue to state the confusing conclusion.

A raised IgE level on its own, even in the absence of parasite infestation is generally not considered a risk factor for transfusion of blood products, but atopic predisposition may be a (non-specific) risk factor.[2] However, there is currently no data to suggest that an IgE cut-off value can be used to confer this risk to recipients of any blood product, including apheresis platelets. Certain donor-related mechanisms may explain IgE-mediated reactions, such as donor food-specific IgE antibodies causing reactions after recipient eats the culprit food, or blood components with penicillin-specific IgE that lead to severe allergic reaction when the recipient is treated with penicillin. The role of direct allergic agonists such as complement 5a and others appears more plausible in this regard.[3] Pre-treatment with antihistaminics and acetaminophen may prevent febrile non-hemolytic transfusion reactions but not severe allergic reactions.[4]

The only test that can be helpful in the setting of suspected anaphylaxis to blood products is mast cell tryptase that should be done either at 1 h or between 2 and 4 h and a definite sample at 24 h post-event (when levels should have returned to baseline). Unless specific trials demonstrate the safety and efficacy of anti-IgE monoclonal antibody therapy in preventing transfusion reactions to blood products, lowering the total IgE level may not have any clinical significance and will simply lead to a significant increase in treatment costs.