Sodium citrate anticoagulation whole blood samples were collected randomly. CD14-phycoerythrin(PE) and CD61-fluorescein isothiocyanate (FITC) were used to label monocytes and platelets. CD62P-PE was used to label activated platelets. The percentages of CD14-PE/CD61-FITC-double-positive MPA in monocytes and CD62P-positive platelets were determined by flow cytometry. Different processing techniques were performed as follows. Whole blood samples were prepared immediately after collection or delayed for different times. After preparation, samples were analyzed immediately or delayed for different times. Antibody immunolabeling was performed before fixation of whole blood samples, immediately after fixation or at different delayed times after fixation. Before immunolabeling, whole blood samples were centrifugated or not. Different antibodies, anti-CD14-PE with anti-CD61-FITC, anti-CD14-PE with anti-CD41-ECD and anti-CD45-ECD with anti-CD61-FITC, were used to label MPA. The results of MPA from different processing techniques were compared.

Compared with immediate preparation after blood collection, the percentages of MPA and CD62P-positive platelets increased with the delayed time at room temperature(18-25℃) and low temperature (2-8℃) (P<0.05), and there was a positive correlation(room temperature: r=0.82, P<0.05; low temperature: r=0.83, P<0.05). Compared with immediate determination after preparation, the percentages of MPA of samples stored at low temperature for 24h after preparation did not alter significantly(P>0.05). Compared with immunolabeling samples before fixation with 1% paraformaldehyde, no significant change was observed in MPA percentages from immediate immunolabeling after fixation or immunolabeling samples stored at low temperature for 24 h after fixation(P>0.05). Centrifugation of whole blood samples before immunolabeling resulted in significant increase of the percentages of MPA and CD62P-positive platelets(P<0.05).MPA percentages resulted from different antibodies had no significant variance (P>0.05).

Whole blood samples should be handled as soon as possible. Fixation with 1% paraformaldehyde at low temperature could store samples for 24h before handling. Centrifugation should be avoided before immunolabeling. After preparation and fixation, samples could be stored at low temperature for 24h before analysis. Different antibody combinations, including anti-CD14-PE/anti-CD61-FITC, anti-CD14-PE/anti-CD41-ECD and anti-CD45-ECD/anti-CD61-FITC, are all suitable for immunolabeling MPA.