低頻度抗原Co^bに対する抗体を保有する一症例

低頻度抗原に対する抗体である抗Co^bは，溶血性輸血反応の原因となることが知られている。今回我々は本邦において症例数の少ない抗Co^bの検出を経験したので報告する。症例は75歳男性，右大腿動脈内膜摘除術目的に当院へ入院となった。術前検査として血液型検査，不規則抗体検査の依頼があり，血液型はA型RhD陽性，不規則抗体検査で陽性となったため同定検査を実施した。検査で陽性を示した赤血球試薬はいずれもCo（b+）であることから不規則抗体抗Co^bの存在が疑われたが，当院では確定できなかったため，日本赤十字社九州ブロック血液センターへ精査を依頼した。後日，不規則抗体は抗Co^bとの報告を受けている。手術に伴い赤血球液4単位の依頼があったが，抗Co^b試薬を常備しておらず，赤血球製剤の抗原検索が困難であり，交差適合試験で陰性となった4単位を準備した。手術中には赤血球液2単位を輸血されたが，明らかな輸血副反応は認めていない。本症例は，不規則抗体スクリーニング，同定検査において抗原表のパターンと合致しない場合には低頻度抗原に対する抗体の存在も念頭に置く必要があることを再確認する症例であった。

The anti-Co^b antibody, an antibody against low-frequency antigens, is known to cause hemolytic transfusion reactions. Here, we report a rare case involving the anti-Co^b antibody. A 75-year-old man was admitted to our hospital for endarterectomy of the right femoral artery. Preoperative examinations for blood typing and irregular antibodies revealed that his blood type was type A and he was positive for RhD. He also showed a positive result in an irregular antibody examination; thus, identification of the antibody was performed. The presence of the irregular anti-Co^b antibody was suspected because all the red blood cell reagents used were Co (b+), which explains the positive result for our patient's serum. Then, we requested confirmation of the typing of the irregular antibody at the Kyushu Block Center of the Japan Red Cross, and the irregular antibody was proved to be the anti-Co^b antibody at a later date. Although there was a request for four units of packed red blood cells for use during surgery, we did not have an anti-Co^b reagent. Therefore, four units of packed red blood cells, which were negative in a cross-matching test, were prepared. Although two units of red blood cells were transfused during the operation, no obvious adverse reactions were observed. From our experience, it is necessary to consider the presence of an irregular antibody to low-frequency antigens when the result of a random antibody screening examination does not match the pattern on the antigen table.