Relationship between glycosylated haemoglobin (HbA1c) and mean plasma glucose

The relationship between plasma glucose and glycosylated haemoglobin is described below:

• the largest set of data relating plasma glucose (PG) to glycosylated haemoglobin (GHB or HbA(1c)) comes from the Diabetes Control and Complications Trial or DCCT (1)
  • the DCCT was a multicenter, randomized clinical trial designed to compare intensive and conventional therapies and their relative effects on the development and progression of diabetic complications in patients with type 1 diabetes
  • quarterly HbA(1c) and corresponding seven-point capillary blood glucose profiles (premeal, postmeal, and bedtime) obtained in the DCCT were analyzed to define the relationship between HbA(1c) and PG.
    • only data from complete profiles with corresponding HbA(1c) were used (n = 26,056)
    • of the 1,441 subjects who participated in the study, 2 were excluded due to missing data
    • Mean plasma glucose (MPG) was estimated by multiplying capillary blood glucose by 1.11
    • linear regression analysis weighted by the number of observations per subject was used to correlate MPG and HbA(1c).
  • Linear regression analysis, using MPG and HbA(1c) summarized by patient (n = 1,439), produced a relationship of:
    • MPG (mmol/l) = (1.98 . HbA(1c)) - 4.29
    • or MPG (mg/dl) = (35.6 . HbA(1c)) - 77.3, Pearson correlation coefficient r = 0.82)
    • among individual time points, afternoon and evening PG (postlunch, predinner, postdinner, and bedtime) showed higher correlations with HbA(1c) than the morning time points (prebreakfast, postbreakfast, and prelunch)

The relationship values of GHB and PG is defined in the table below:

* Mean blood glucose results are 10-15% lower. Most blood glucose meters are calibrated to read as plasma glucose.

Reference:

1. New Engl J Med 1993;329:977-986
2. Diabetes Care. 2002 Feb;25(2):275-8.