Abstract: Objective To discuss the necessity of grey area in HIV screening experiment of ELISA. Methods The blood sample which was reactive in the preliminary screening from 2012 to 2016 were sent to the HIV confirmation laboratory. The Results of preliminary screening were analyzed retrospectively according to S/CO value. ResultFrom 2012 to 2016,165189 cases blood donors were detected. 630 cases were reported to HIV confirmation laboratory by double reagent reactive or single reagent was double reactivity. Positive Results were confirmed in 96 cases.514 cases were reactive in the reagent of Sorin. 115 cases of S/CO value in the 0.8-1.0 interval were negative. 239 cases were reactive in the reagent of Jinhao. 17 cases of S/CO value in the 0.8-1.0 interval were negative. Conclusion To set the grey area in the HIV screening test by ELISA is unnecessary.

Key words: HIV, Retrospective analysis, Grey area