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.