Deposition of C4d on the surface of RBCs from trauma patients and healthy donors was measured by flow cytometry and mean fluorescence intensity. A, Representative flow cytometry experiment. B, we used samples from 102 trauma patients (n, 0 hour =102, 6 hour =24, 24 hour =35 and 72 hour =19) and 30 samples from healthy donors (HD). The mean fluorescence intensity [Mean ± SD (min - max)] of C4d deposition on the surface of RBCs was [2278 ± 1504 (94 – 5631)] for healthy donors, [5325 ± 2941 (1113–15683)] for 0 hour, [5254 ± 1862 (1698 – 7687)] for 6 hour, [5306 ± 1988 (1245 – 9462)] for 24 hour and [5074 ± 2444 (1802 −11346)] for 72 hour patients.