The relationship between self-monitoring of blood glucose results and glycated haemoglobin in type 2 diabetes: The Fremantle Diabetes Study

The benefits of self-monitoring of blood glucose (SMBG) in type 2 diabetes remain contentious. If SMBG data do not accurately reflect HbA1c, attempts to modify lifestyle/pharmacotherapy will be ineffective. We aimed to determine how well SMBG correlates with HbA1c and fasting serum glucose (FSG). Community-based type 2 patients using SMBG provided their highest and lowest pre- and post-prandial glucose results in the week before detailed assessment. The ability of average pre- and post-prandial SMBG to predict HbA1c > 7.0% was determined by linear regression and receiver operating characteristic (ROC) analyses. Of 1286 patients with known SMBG status, 70% reported using SMBG. Pre-prandial SMBG data were obtained from 554 participants and post-prandial SMBG data from 418. The mean SMBG result and HbA1c correlated significantly (pre-prandial rs = 0.55, post-prandial rs = 0.47; P < 0.001). Areas under the ROC curve (95% confidence limits) were 0.78 (0.74-0.83) and 0.74 (0.69-0.78) for pre- and post-prandial SMBG (P < 0.04). The optimal cut-point was 6.5 mmol/L for pre-prandial SMBG (sensitivity 79.3%, specificity 64.4%). Mean pre-prandial SMBG results correlated with FSG (rs = 0.64, P < 0.001) but were on average 1.4 mmol/L lower, consistent with known whole blood vs. plasma differences. Since SMBG values reflect prevailing glycaemia, refinements in their interpretation and application may improve SMBG effectiveness.