Saint Louis University School of Medicine 1 article published in JoVE Immunology and Infection Measuring Deformability and Red Cell Heterogeneity in Blood by Ektacytometry Nermi L. Parrow*1, Pierre-Christian Violet*2, Hongbin Tu2, James Nichols3, Corinne A. Pittman4, Courtney Fitzhugh4, Robert E. Fleming1,5, Narla Mohandas6, John F. Tisdale3, Mark Levine2 1Department of Pediatrics, Saint Louis University School of Medicine, 2Molecular and Clinical Nutrition Section, Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, 3Molecular and Clinical Hematology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, 4Sickle Cell Branch, National Heart, Lung and Blood Institute, National Institutes of Health, 5Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, 6Red Cell Physiology Laboratory, New York Blood Center Here we present techniques to measure red cell deformability and cellular heterogeneity by ektacytometry. These techniques are applicable to general investigations of red cell deformability and specific investigations of blood diseases characterized by the presence of both rigid and deformable red cells in circulation, such as sickle cell anemia.