© 2019 De Gruyter. All rights reserved.Objective: Medical laboratories encounter critical obstacles in External Quality Assessment (EQA) practices that are key to assessment of the analytical period. Present study aims to unveil the challenges in nationwide interlaboratory harmonization and suggest practical solutions. Materials and methods: EQA results of 1941 laboratories participating in 18 different EQA-programs between 2010 and 2017 were examined. Standard Deviation Index (SDI) of each program calculated using 801,028 sample data from 24 different clinical chemical tests were used to conduct a process assessment. Results: There is a significant discrepancy in unsatisfactory performance ratio among different EAQ-programs with an average of 3.4% (27,074 cases) between 2010 and 2017 and a decreasing trend (~40-50%) in 7-years. Programs with higher SDI display lower discrepancy rates. Reasons for unaccepted results appear to be data entry errors (8.27-22.2%), material dilution errors (5-11.4%), technical problems (3.76-7.9%); while random or unidentified causes account for a major of 44.9-59.5%. In 7-years, 15.7% reduction was observed in average SDI of all tests. Conclusion: With the launch of national EQA follow-up program, increased awareness of the analytical processes led to a decrease in unaccepted results and variances in the analytical period. Staff training is suggested as a significant measure. In addition, simultaneous assessment of SDI and allowable total error rates would reduce the variation between programs.