In order of their strong immunogenicity, D, K, C, E, k, and e, are clinically important blood group antigens outside the ABO system . In particular, the anti-K antibody has the second strongest immunogenicity after the anti-D antibody. The anti-K plays a critical role in transfusion reactions or hemolytic disease of the fetus and newborn after alloimmunization. The expression of blood group antigens is different among different ethnic groups. The K antigen is rarely expressed in Koreans. Thus, the clinical importance of the anti-K is very low. On the other hand, in proportion to the increase in immigrants from all over the world, the distribution of blood group antigens has changed in recent years. This study investigated the prevalence of the Kell group antigens according to their parents’ birth region.
Participants aged <30 years living in Korea were recruited regardless of nationality. The participants self-identified their parents’ birth region. They were classified into a Korean group (both parents born in Korea and of Korean ethnicity), an East Asia group (at least one parent born in East Asia and of non-Korean ethnicity), and a group of ‘Others’ (at least one parent born in America, Europe, South Asia, or other countries, and of non-Korean ethnicity). The Institutional Review Board of the Pusan National University Hospital approved the study protocol (approval number: H-1509-001-033). Antigen typing was performed using the Antigen profile II (Bio-Rad, Cressier, Switzerland) and Anti-K (Diagast, France) using a manual technique. Testing and interpretation were performed according to the manufacturer’s recommendation. Data were analyzed using IBM SPSS Statistics 22 (International Business Machines Corp., Armonk, NY, USA). Comparisons were performed using the Pearson’s Chi-squared test and Fisher’s exact test.
Four hundred and eighty-seven participants were recruited in the study. Five (4.0%) participants in the group of ‘Others’ expressed the K antigen. Both parents were born in America (n=1), Europe (n=2), or South Asia (n=2). No participants in the Korean or East Asia groups expressed the K antigen. No participants expressed the Kpa antigen. All participants expressed the k and Kpb antigens (Table 1).
In this study, the participants of Korean ethnicity did not express the K antigen. On the other hand, 4% of participants with a parent born in America, Europe, and South Asia expressed the K antigen. This result was consistent with previous reports. Owing to the ethnic diversity of blood group antigen expression, almost none of the Koreans had the K antigen. In contrast, approximately 9% and 1.5% of individuals of Caucasian and African descent expressed the K antigen, respectively [2,3]. Approximately 1.97∼8% of individuals expressed the K antigen in South Asia [4,5]. The Kpa has a frequency of 2% in Caucasians and 0% in African and Japanese, whereas k and Kpb have high frequencies in all ethnic groups . This study also showed that no participants expressed Kpa antigen while all participants expressed the k and Kpb antigens.
Until now, the prevalence of the K antigen in Korea is very low. The chance of alloimmunization to K is barely considered. Because blood donation by non-Koreans in Korea is possible and interracial marriage is increasing, the possibility of exposure to K antigen is increasing. Therefore, whenever a blood donor with an ethnic origin belonging to the group of ‘Others’ donates blood, the expression of the K antigen should be determined. According to the guidelines of the Royal College of Obstetricians and Gynaecologists for monitoring fetal newborn hemolytic disease, antibody titers are tracked for anti-K antibodies and anti-E with anti-c . Because of the clinical significance of anti-K in pregnancy, K- girls and women of childbearing age should be transfused with K- blood. If testing for the K antigen is not possible, individuals who might express the K antigen should donate platelets and plasma, but not red blood cells.
In conclusion, with the increasing number of immigrants in Korea, the possibility of finding individuals expressing the K antigen has increased. When individuals with the K antigen participate in blood donation, the frequency of the anti-K in transfusion recipients will change. Owing to the strong immunogenicity of the K antigen, it is necessary to consider the K antigen frequency and anti-K in Korea.