BACKGROUND: A1c, a surrogate measure of glycemic control, is known to have a 
strong linear correlation with mean plasma glucose (MPG) when analyzed in 
populations of patients. However, clinically significant intersubject 
variability in this relationship exists, which suggests that A1c measurements 
may not reflect actual glycemic control in some patients. In the present study 
we explored the extent to which A1c accurately represents glycemic control, as 
measured by MPG, for individual patients.
METHODS: Data were pooled from randomized clinical trials in which A1c and 
self-monitored plasma glucose (SMPG) profiles were collected by patients with 
Type 2 diabetes treated with insulin analog regimens. MPG levels were calculated 
from SMPG profiles. Distributions of MPG were analyzed for patients within 
similar ranges of A1c (<6.5%, 6.5%-<7.5%, 7.5%-<8.5%, 8.5%-<9.5%, and ≥9.5%) and 
distributions of A1c were analyzed in patients within similar ranges of MPG 
(<6.1, 6.1-<7.8, 7.8-<9.4, 9.4-<11.1, and ≥11.1 mmol/L).
RESULTS: Substantial proportions of patients had clinically significant 
differences between A1c and MPG. For example, among 260 patients with A1c 
between 6.5% and 7.5%, 10% had MPG levels <6.4 mmol/L, whereas 10% had MPG >9.5 
mmol/L. Among the 224 patients with MPG levels ≥6.1 mmol/L and <7.8 mmol/L, 10% 
had A1c <6% and 10% had A1c >8.1%.
CONCLUSIONS: In the absence of SMPG, A1c may inadequately represent glycemic 
control for many diabetic patients.