Confirmation and analysis of the cut-off value in anti-HIV and anti-TP ELISA kits for blood donation screening

Objective To evaluate the necessity of the application of Youden index in the cut-off value(S/CO)determination and the gray zone range establishment in anti-HIV and anti-TP ELISA kits for blood donation screening.Methods Data was collected from the project organized by the National Center for Clinical Laboratories to evaluate anti-HIV and antiTP ELISA kits by multiple centers and was analyzed by the SPSS[17.0] system.The Youden index under different S/CO value was calculated with the equation where Youden index =sensitivity+ specificity-1.Each curve was plotted with the S/CO value on the horizontal axis and Youden index on the vertical.Thus the optimal S/CO values were defined as the Youden index values reacbe maximum.Results Among 7 different anti-HIV ELISA kits provided,one presented a maximum Youden index value at a S/CO value of 1 while the rest possessed maximum Youden index values at S/CO values of 5.As far as the 5 anti-TP ELISA kits being concerned,the Youden indexes reaches maximum values at S/CO values of 1 (2 kits),3 (2kits) and 5 (1 kit).Conclusion Since the sensitivity and specific of 7 anti-HIV ELISA kits and 5 anti-TP ELISA kits all reaches optimal when S/CO ≥ 1,there is no need to set gray zone range for these two kinds kits evaluated.