BACKGROUND: The assessment of glycemic control, most commonly using glycosylated 
hemoglobin (A1C), has been a major measure for care of patients with diabetes. 
Historically, dichotomous thresholds have been set for intermediate outcomes 
such as A1C (in this case, > 9%) on the basis of levels associated with high 
risk, that is, thresholds for what would be considered poor control for all 
persons.
LIMITATIONS AND POSSIBLE UNINTENDED CONSEQUENCES OF THRESHOLD MEASURES: 
Dichotomous threshold measures may not accurately reflect the true impact of 
care on population health because absolute risk reduction for micro- and 
macrovascular complications of diabetes is not linear but rather log-linear, 
with greater impact of a given improvement on patients with worse rather than 
better glycemic control. Also, an "all or none" measure for all patients set at 
"optimal" control may unfairly evaluate physician/health care performance.
A CONCEPTUAL MODEL FOR ASSESSING THE QUALITY OF GLYCEMIC CONTROL: A continuous 
measure of A1C, as the cornerstone in quality assessment for diabetes, can 
incorporate each of the Institute of Medicine's (IOM)'s quality domains: 
effectiveness and equity, patient safety, patient-centered care, timeliness, and 
efficiency.
CONCLUSIONS: A continuous measure of A1C can better capture than a dichotomous 
measure the complexity of glycemic control at a population level.