The NGSP consists of a Steering Committee and a network of reference laboratories including the Central Primary Reference Laboratory (CPRL), backup Primary Reference Laboratories (PRLs) and Secondary Reference Laboratories. The CPRL and PRLs analyze HbA1c using the Bio-Rex 70 cation-exchange assay method used in the Diabetes Control and Complications Trial (DCCT). The SRLs work directly with manufacturers and laboratories to assist them in calibrating their methods, and provide data for certification of traceability to the DCCT. The SRLs are monitored monthly against the CPRL monthly, and the NGSP network is monitored against the IFCC Laboratory Network two times per year, via sample comparisons. The effectiveness of the NGSP program in harmonizing HbA1c results is assessed via the College of American Pathologists (CAP) GH-2 whole blood survey performed twice a year.