Bombay blood group: Is prevalence decreasing with urbanization and the decreasing rate of consanguineous marriage

CONTEXT: Bombay blood group although rare is found to be more prevalent in the Western and Southern states of India, believed to be associated with consanguineous marriage. AIMS: To estimate the prevalence of the Bombay blood group (Oh) in the urban population of Puducherry. To find the effect of urbanization on consanguineous marriage and to establish whether consanguinity plays a part in the prevalence of Oh group. To compare Oh group prevalence with that of other neighboring states, where population is not predominantly urban. SETTINGS AND DESIGN: This is a descriptive study in a tertiary care hospital in Puducherry, over a period of 6 years. MATERIALS AND METHODS: All blood samples showing 'O' group were tested with anti-H lectin. Specialized tests like Adsorption Elution Technique, inhibition assay for determination of secretor status were performed on Oh positive cases. Any history of consanguineous marriage was recorded. STATISTICAL ANALYSIS USED: All variables were categorical variable and percentage and proportions were calculated manually. RESULTS: Analysis of the results of 35,497 study subjects showed that the most common group was 'O' group constituting 14,164 (39.90%) of subjects. Only three "Oh" that is, Bombay phenotype (0.008%) were detected. Consanguinity was observed in two cases (66.66%). CONCLUSIONS: This study shows the prevalence of Bombay blood group representing the urban population of Puducherry, to be high (0.008%) and associated with consanguineous marriage (66.66%). Thus, consanguinity is still an important risk factor present, even in an urban population in Southern India.