Identification and Diagnosis of Complete Haptoglobin Gene Deletion, the Gene Responsible for Adverse Posttransfusion Reactions

Abstract

Allergic reactions are the most frequent adverse effects of blood transfusion, and anaphylactic shock, although less frequent, is systemic and serious. The causes of allergic reactions to blood transfusions are largely unknown, but deficiencies in serum proteins such as haptoglobin (Hp) can lead to anaphylactic shock. A complete deletion of the haptoglobin gene (HPdel) was first identified in families with anomalous inheritance and then verified as a genetic variant that can cause anaphylactic shock because homozygotes of HPdel have an Hp deficiency. Thereby, they may produce antibodies against Hp from blood transfusions. HPdel is found in East and Southeast Asian populations, but not in other populations, with a frequency of approximately 0.9% to 4%. Diagnosis of Hp deficiency due to HPdel prior to transfusion is desirable because severe adverse reactions can be prevented by washing the red blood cells and/or platelets with saline or by administrating plasma products obtained from an Hp deficient donor pool. This review outlines the background of the identification of HPdel and several genetic and immunological methods developed for diagnosing Hp deficiency caused by HPdel.