HbA1c, blood glucose monitoring and insulin therapy

Safe adjustment of insulin therapy requires review of both long-term and short-term glycaemic control, HbA1c and blood glucose monitoring (BGM), respectively.

To summarise the information that HbA1c and BGM provide about glycaemic control and to outline how to use these measures to guide insulin therapy.

There are three components to the 24-hour blood glucose profile: 1. the flat baseline set by the fasting blood glucose 2. often a daytime increment in this baseline 3. the prandial blood glucose increase. Insulin therapy aims to sequentially control each component to achieve a desired level of glycaemic control (usually HbA1c <7%). Clinical use of the two glycaemic measures requires that BGM results are not highly variable (which complicates safe insulin adjustment) and that both BGM and HbA1c results are reliable. If these conditions are met and there is a discrepancy between the BGM profile and the average blood glucose expected from the measured HbA1c, there may be periods of undetected hyper- or hypoglycaemia over the 24-hour period, which require changes in insulin therapy.