IMMUNOHEMATOLOGY, VOLUME 14, NUMBER 1, 1998 22 K (Kell) is one of the most immunogenic of the red blood cell (RBC) antigens. In order to select K- RBC units, we developed K pheno- typing on the Olympus PK-7200 equipment to save labor, time, and costs. The Olympus PK-7200 is fully automated equipment used pri- marily for blood typing and syphilis screening. We tested 3,587 blood donor samples in EDTA using a commercial anti-K serum dilut- ed in HP Hemagen Power Solution R (1:40). The equipment was set to prepare a 1.7% RBC suspension in bromelain and to dispense 25μL of the mixture (diluted serum and HP Hemagen Power Solution R ) in terraced microplates. After mixing, the microplates were incubated for 1 hour at 30°C. Reading was performed by a C.C.D. camera and the results were automatically transferred to the mainframe comput- er. We found 185 K+ blood samples and 3,402 K- samples. Four sam- ples, K+ by the PK-7200, were confirmed as K- by tube test. The use of bromelain with the PK-7200 may have caused the falsely positive tests. The Olympus PK-7200, used for K phenotyping, saves labor time and costs. It also reduces handling and thus promotes less con- tamination risk for laboratory personnel. Immunohematology 1998;14:22–25. Key Words: automation, phenotyping, Kell blood group Anti-K (Kell) is the most common immune red blood cell (RBC) antibody outside the ABO and Rh blood group systems. 1 Many severe hemolytic transfusion reactions due to anti-K have been described, and it has been implicated in severe cases of hemolytic disease of the newborn. 2 Kell blood group system antigen frequencies present important variations depending on ethnic origin. 3 The K antigen is present in approximately 9 percent of whites and in only 2 percent of North American blacks. 4 It is extremely rare in Mongoloid people of eastern Asia. 5 The highest K antigen frequency is observed among people of the Arabian and Sinai peninsulas, where up to 25 per- cent may be K+. 6 The K/k gene frequency has been studied in differ- ent populations. In Brazilian blood donors, K/k gene frequencies are: in whites, K = 0.0462 and k = 0.9574; in blacks, K = 0.0181 and k = 0.9819; genotype fre- quencies are: K/K = 0.0021, K/k 0.0881, and k/k = 0.9097. 7 The K antigen is usually determined using an antiglobulin method. 8 However, there are unusual K and k phenotypes that require adsorption and elution studies in order to confirm true RBC phenotypes. 9 The weak expression of the K antigen is a rare event that occurs in the McLeod and Gerbich-negative pheno- types. 10 It can be detected also in a variety of pheno- types in which all high-frequency Kell and para-Kell antigens are depressed. 1 There is a case report of a patient previously known to be K-k+ who became K+, as did transfused K- RBCs. 11 A gram-positive organism, Streptococcus faeci- um,was detected in the patient’s blood culture.K- RBCs incubated in vitro with a culture containing S.faecium also were converted to K+. Because of its clinical signif- icance, K phenotyping is performed in many blood banks for transfusion purposes. 7 The method used for K phenotyping depends on the number of donations per day and the need for K typing.The test can be performed by tube, microplate, gel test, capillary techniques, manu- ally, or using automated equipment. 12,13 Since 1963, when preliminary automated blood typing results were published by MacNeil et al., 14 other equipment has been developed for routine blood banking applications. These are semi- or fully automated analyzers.All of them include a micropro- cessor or a microcomputer, giving greater flexibility and easier handling of data. 15,16 They can be used not only for ABO/Rh blood group typing but also for phe- notyping other blood group antigens 17 and for anti- body detection. 18 We describe here our experience phenotyping for the K antigen using PK-7200 automated equipment. Basic characteristics include automated sample recognition, dispensing of reagents, incubation and settling, reading, interpretation, and printing of the results. 19 Materials and Methods Samples From March to April 1996, 3,587 EDTA-anticoagulated blood donor samples were phenotyped for the K anti- gen in a PK-7200 automated analyzer (Olympus America, K phenotyping using a PK-7200 automated analyzer M.C.Z. NOVARETTI, S.P. NAVARRO, P.E. DORLHIAC-LLACER, AND D.A.F. CHAMONE