Reddenna, L., P. Venkatesh, K. S. Kumar, and A. S. K. Reddy. “H/H Blood Group System: A Rare Blood Group”. PharmaTutor, Vol. 5, no. 9, Sept. 2017, pp. 69-71, http://www.pharmatutorjournal.com/index.php/pt/article/view/472.