Modifications in erythrocyte membrane protein content are not responsible for the alterations in rheology seen in sepsis.

Red blood cell (RBC) rheology is altered in sepsis and may contribute to the microcirculatory alterations in these patients, but the mechanisms of these changes are not well defined. An increase in the RBC protein band 3/α-spectrin ratio has been observed in a mouse model of septic shock, suggesting a possible alteration in the RBC membrane integral/peripheral protein ratio. This protein modification could contribute to the alterations in RBC rheology observed in sepsis. As there are interspecies differences in membrane composition, these observations need confirmation in humans. We studied RBCs from healthy volunteers (n = 10) and from patients with (n = 15) and without (n = 9) sepsis within 24 h of intensive care unit admission and also on day 3 for the septic patients. Exclusion criteria were recent RBC transfusion, hematologic diseases, cirrhosis, and diabetes mellitus. Procedures included screening for alterations in RBC membrane proteins using cryohemolysis and separation of RBC membrane and skeletal proteins by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The hemogram, including reticulocyte count, was similar between nonseptic and septic patients on day 1. The majority of RBC membrane protein ratios, including band 3/spectrin, were more elevated in critically ill patients (nonseptic and septic) than in volunteers, but RBC membrane skeletal protein content was similar in septic and nonseptic patients. There were no significant differences in cryohemolysis results among groups. Alterations in RBC rheology in sepsis are therefore mainly due to alterations in membrane compounds other than skeletal proteins, like carbohydrates, such as sialic acid and/or lipids.