Effects of sample temperature on red blood cell shape in septic patients

Several recent in vitro studies have observed that alterations in red blood cell (RBC) rheology depend on sample temperature. This possibility could limit the in vivo validity of the assessment of RBC shape. We investigated the effects of sample temperature on RBC shape estimated by flow cytometry in septic patients compared with those of volunteers. 0.5 ml of blood was placed at 4 degrees C, room temperature (20 degrees C) or at 37 degrees C. RBCs were analyzed at 30 minutes (T30) by flow cytometry and results compared to baseline measures. With the flow cytometry technique, the RBC shape of healthy volunteers shows a bimodal distribution related to the biconcave form. On this histogram, we calculated the second Pearson coefficient of dissymmetry--PCD--representing the asymmetry of this histogram. At baseline, RBC PCD was increased in septic patients representing a more spherical shape compared to volunteers (-0.73+/-0.18 versus -0.95+/-0.05; p=0.007). For both groups, RBC shape estimated by the flow cytometry technique was not modified by the temperature of the sample. We conclude that estimation of RBC shape by flow cytometry is not influenced by the temperature of the sample. The present study validates the flow cytometry technique to assess RBC shape in vitro.