According to the largest Youden Index, a specific optimal cut-off value generated by receiver operating characteristic (ROC) curve analysis was often to be used to predict G6PD deficiency and evaluate for diagnostic accuracy based on sensitivity, specificity, and the area under the ROC curve (AUC), having to discriminate all patients with G6PD levels accurately below a preset cut-off value, which is often followed with manufacturer's protocol. Here, G6PD is linked to G6PD deficiency.