ObjectiveThe aim of this study is to investigate change of platelet count in red blood cell （RBC） units at different storage periods and explore the efficiency of platelet removal by leukocyte filter. MethodsA total of 58 RBC units were divided into four groups according to different storage periods： 1 week Group （16）， 2 weeks Group （16）， 3 weeks Group （14） and 4 weeks Group （12）. RBC units in the four groups were filtered through leukocyte filter. The RBC samples before and after filtration were obtained. The platelet count was detected by automatic blood cell counter and the efficiency of platelet removal was calculated. RBC samples before filtration were made into blood cell smears. The blood cell smears were dyed with Wright-Giemsa stain， and the morphology of platelets was observed through a microscope. ResultsThe platelet count in RBC units stored for 1， 2， 3 and 4 weeks was （286.5±62.34）×10⁹/L， （238.0±57.37）×10⁹/L， （193.6±56.21）×10⁹/L and （167.8±24.76）×10⁹/L， respectively. Platelet count in blood stored for 3 weeks （P<0.01） and 4 weeks （P <0.000 1） were significantly lower than those stored for 1 weeks. When observed in the blood smears of RBC units at different storage periods， platelets with normal morphology were distributed in clump and scattered style. The platelet removal rates of the four groups were （80.13±9.06） %， （76.41±10.13） %， （77.78±9.30） % and （70.63±9.39） %， respectively， with no significant difference （P >0.05）. ConclusionsPlatelet count in RBC units decreases gradually as the storage period increases， but most platelets still remain in RBC units of late storage periods （3 weeks and 4 weeks）. The leukocyte filter is able to remove most of the platelets， and the removal efficiency is similar among the groups.