Variability in the relationship between mean plasma glucose and HbA 1c: Implications for the assessment of glycemic control

Eric S. Kilpatrick, Alan S. Rigby, Stephen Atkin

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Background: Previous studies have shown a single linear relationship between mean plasma glucose (MPG) and hemoglobin A1c (HbA 1c). We examined the relationship in different treatment groups of patients with type 1 diabetes participating in the Diabetes Control and Complications Trial (DCCT). Methods: Seven-point glucose profiles (premeal, postmeal, and bedtime) and HbA1c were measured quarterly during the DCCT. We studied measurements from (a) intensively treated patients at study commencement, (b) intensively treated patients after stabilization of their glycemia (from 6 months onward), and (c) conventionally treated patients from 6 months onward. Only complete glucose profile and HbA1c pairings were considered (n = 589, 11 483, and 11 855, respectively). Results: From 6 months into the trial, conventionally treated patients had consistently higher MPG concentrations than intensively treated patients at any given HbA1c value (mean difference, 1.6 mmol/L at 7% HbA1c, increasing to 2.8 mmol/L at 11% HbA1c). Similarly, at the same HbA1c, the MPG of intensively treated patients at baseline was higher than in the same individuals after 6 months of intensive treatment (1.2 mmol/L difference at 7% HbA1c, increasing to 4.6 mmol/L at 11% HbA1c). Conclusions: The relationship between MPG and HbA1c is not constant but differs depending on the glycemic control of the population being studied. Having lower mean glucose at the same HbA1c may help explain why intensive DCCT treatment appeared intrinsically linked to both increased hypoglycemia and decreased microvascular complications compared with conventional treatment. These findings may also have implications for expressing HbA1c as mean blood glucose equivalent.

Original languageEnglish
Pages (from-to)897-901
Number of pages5
JournalClinical Chemistry
Issue number5
Publication statusPublished - May 2007
Externally publishedYes


ASJC Scopus subject areas

  • Clinical Biochemistry
  • Biochemistry, medical

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