Clin. Lab. 6/2021 1 Clin. Lab. 2021;67:XXX-XXX ©Copyright ORIGINAL ARTICLE Prevalence of Kell Blood Group System in Blood Donors of Makkah City, Saudi Arabia Ammar Khojah 1, # , Raed Felimban 2, 4, # , Saeed Kabrah 3 , Mansour Alqasmi 1 # Contributed equally to the work 1 Laboratory and Blood Bank Department, AlNoor Specialist Hospital, Makkah, Saudi Arabia 2 Department of Medical Laboratory Technology, Faculty of Applied Medical Sciences, King Abdulaziz University, Jeddah, Saudi Arabia 3 Laboratory Medicine Department, Faculty of Applied Medical Sciences, Umm Al-Qura University, Makkah, Kingdom of Saudi Arabia 4 Center of Innovation in Personalized Medicine (CIPM), King AbdulAziz University, Jeddah, Saudi Arabia SUMMARY Background: The Kell blood group system has different types of antigens, which have immunogenic properties; therefore, it is considered as the third clinically significant blood group in blood transfusion. Patients that lack Kell antigen may produce antibodies that may cause transfusion reaction. This study is the first report on Kell an- tigen system distribution in blood donors in Makkah city which is important to improve transfusion services. Therefore, the aim of the current study is to determine the distribution of Kell antigens and phenotypes among blood donors in Makkah city, Saudi Arabia. Methods: This is a retrospective study to determine the prevalence of Kell antigens among blood donors, who come to donate blood in Al Noor specialist hospital, Makkah city. The sample size was 150 donors with a mini- mum age of 18 years. Results: The most common Kell antigens were k antigen (96%) and Kpb (98%), while the less common were K an- tigen (18.7%) and Kpa (3.3%). The two most common Kell phenotypes are Kp(a-b+) (95%) and K-k+ (79.3%), while the two least common Kell phenotypes are Kp(a-b-) (1.3%) and Kp(a+b-) (0.6%,). Conclusions: This is the first study that set out to determine the prevalence of Kell antigens and phenotypes among blood donors in Makkah city. This study showed that there is a variation in Kell antigen and phenotype distribution. The Kell blood group system has an important impact on transfusion medicine. (Clin. Lab. 2021;67:xx-xx. DOI: 10.7754/Clin.Lab.2020.200946) Correspondence: Dr. Raed Ismail Felimban Department of Medical Laboratory Technology Faculty of Applied Medical Sciences King Abdulaziz University P.O. Box 80216 Jeddah, 21589 Saudi Arabia Phone: +966 (12) 6400000 Ext. 51526 Mobile: +966 553122885 Email: faraed@kau.edu.sa _______________________________________________________ Manuscript accepted November 19, 2020 KEY WORDS prevalence, Kell, antigens, phenotypes, donors, Makkah INTRODUCTION The primary goal of blood transfusion services is to pro- vide the patient with compatible red blood cells (RBCs) that can survive and function for a longer time after transfusion. This will give the patients the benefit of blood transfusion. To achieve this goal, blood doQRUVｶ 5%&V VKRXOG EH FRPSDWLEOH ZLWK SDWLHQWVｶ EORRG W\SH The criteria for selecting blood donors depends on the absence of antigens in their RBCs for antibodies in pa- tients serum needing transfusion after antibody screen- ing and identification have been performed [1]. Deter-