Feasibility of centralized measurements of glycated hemoglobin in the Diabetes Control and Complications Trial: a multicenter study. The DCCT Research Group.

A method for measuring glycated hemoglobin (Hb A1c) and an accompanying method of specimen transport to a central laboratory were developed for the multicenter Diabetes Control and Complications Trial (DCCT). In the DCCT, results for Hb A1c are used to assess chronic glycemic control for data collection and patient management. During the feasibility phase of the trial, central (CHL) and backup laboratories using automated, "high-performance" ion-exchange liquid-chromatographic methods were established. Whole-blood samples were stored (4 degrees C) at each of the 21 clinical centers for up to 72 h before air-express shipment to the CHL. Quality-control procedures included daily analyses of three calibration specimens. A pooled hemolysate was assayed frequently over time as a long-term quality control (LTQC). After 18 months, within- and between-run CVs were less than 6%. Mean values for split duplicate samples assayed in a masked fashion at the CHL were nearly identical. LTQC results indicated no significant assay drift over time. More than 6000 samples were assayed (mean interval between obtaining the blood sample and completing the assay: less than six days). Hb A1c evidently can be precisely and reliably measured in the context of a long-term, multicenter trial such as the DCCT.