Evaluation for serum glucose standardization in clinical laboratories of Southern China by consecutive 6 years proficiency testing based on JCTLM-recommended reference methods oleh Lin Xueying, Yan Qiaofang, Du Yuanyuan, Wang Jianbing, Huang Di, Yan Jun, Zhan Min, Zhang Pengwei, Cheng Jingyu, Zhang Qiaoxuan, Huang Xianzhang, Han Liqiao