A study of the Lewis blood group system in the Singapore population.

The purpose of this retrospective study is to delineate: a) The ethnic group specific distribution patterns of the various Lewis phenotypes in our population in Singapore. b) The occurrence rates of the various anti-Lewis antibodies in our population. The approximate frequencies of the Lewis A-B-, Lewis A-B+ and Lewis A + B- phenotypes in the blood-donor population were estimated to be about 10%, 48% and 42% respectively. It was evident that frequency of the Lewis A-B- phenotype was highest among the Malays, being almost 3 times more frequent than it was among the Chinese (P less than 0.01). The anti-Lewis antibodies were noted to be the commonest irregular antibodies seen in our blood donor population, with an occurrence rate of about 127 per 100,000. Likewise, from 1982 to 1987, the anti-Lewis antibodies were also noted to be the most frequently encountered antibodies in our patient population, accounting for nearly 60% of all cases. Although the Malays comprised only about 15% of the Singaporean population, they accounted for as much as 42.9% of all patients with anti-Lewis antibodies. Similarly, out of all 76 blood donors in 1987 with anti-Lewis antibodies, 50% were found to be Malays although they comprised only 14.28% of the donor population. It was also interesting to note that a sizeable proportion of all patients with anti-Lewis antibodies were pregnant women with or without obstetric complications.