A total of 5 × 7 ml heparin blood tubes were collected from each of seven donors, and 2 × 7 ml heparin blood tubes from an additional donor. Individual tubes were either processed immediately or kept at RT or 4°C for 6 or 24 h. PBMCs and an aliquot of whole blood were analysed using a Sysmex XP-300™ Automated Hematology Analyzer. These full blood counts were analysed using a one-way mixed effects ANOVA with post-hoc Tukey’s tests. A small drop in WBC was seen with RT storage (5% at 6 h, 11% at 24 h, P=0.04) and a larger drop at 4°C (12% at 6 h P=0.003, 25% at 24 h P=0.002). For the additional donor, only the 0 and 24 h RT analyses were performed. Cell recovery of (A) WBC and (B) lymphocytes was calculated as a percentage of the cell number loaded on to the Ficoll-hypaque gradient. Missing values for lymphocytes are due to the inability of the Sysmex to resolve a distinct lymphocyte peak. Data were analysed using a one-way mixed effects ANOVA with post-hoc Tukey’s tests and P values indicating significant differences between the timepoints are shown. For the 4°C analysis, a 24-h lymphocyte count was obtained for only a single sample, so the 0- and 6-h timepoints were analysed using a paired values t test.