Anaphylactic transfusion reactions in haptoglobin-deficient patients with IgE and IgG haptoglobin antibodies

BACKGROUND : Patients with haptoglobin deficiency associated with haptoglobin IgG antibodies, who experienced severe nonhemolytic transfusion reactions (NHTRs), have been identified in Japan. Haptoglobin deficiency therefore might be a risk factor for NHTRs. STUDY DESIGN AND METHODS : A total of 4138 cases of voluntarily reported NHTRs in Japan, including 367 cases of immediate‐onset anaphylactic NHTRs, were examined to identify haptoglobin deficiency. Serum haptoglobin IgG and IgE antibodies were determined in haptoglobin‐deficient patients to elucidate the mechanism underlying the transfusion reactions. RESULTS : Seven patients with haptoglobin deficiency were identified. Six of them experienced severe and acute NHTRs. Six of them were identified to be homozygous for the Hp del allele of the haptoglobin gene. Both haptoglobin IgG and IgE antibodies were detected in serum samples of all the patients. The stimulative effects of blood transfusion on the production of hap‐ toglobin antibodies in the patients and the relation‐ ship between the presence of the antibodies and the occurrence of the transfusion reactions were observed. CONCLUSION : Anaphylactic NHTRs in these patients with haptoglobin deficiency associated with serum haptoglobin antibodies were suggested to be prevalent in Japan. In addition to IgG antibodies, IgE haptoglobin antibodies detected in the sera of such patients were suggested to play a role in the occurrence of the reactions.