ASSESSING THE VALIDITY OF RANDOM BLOOD GLUCOSE TESTING FOR MONITORING GLYCEMIC CONTROL AND PREDICTING HbA1c VALUES IN TYPE 2 DIABETICS AT KARL BREMER HOSPITAL
Background: The number of adults affected by diabetes mellitus in developing countries, such as South Africa, is projected to grow by 170%, from 84 to 228 million people between 1995 and 2025 .This high and increasing prevalence of diabetes worldwide, and the economic burden of diabetes on developing countries like South Africa emphasizes the importance of ensuring good glycemic control so as to slow down the rate of disease progression and prevent complications. The district health care facilities are the foundation of the health care system of South Africa. The current practice is that diabetics have a point of care random blood glucose (RBG) done on the morning of their clinic appointment and this is used as a form of assessment of glycemic control during the consultation. For further clinical decision making a HbA1c is done once a year as a benchmark of glycemic control. The practical clinical question that arises is whether the assumptions underlying local clinical decision making using the RBG are valid and to what extent RBG can be used to guide clinical management. Aim and Objectives: The aim of this study was to assess the strength of the correlation between RBG and HbA1c and to make recommendations for the interpretation of RBG results in adult patients with Type 2 Diabetes taken at Karl Bremer District Hospital out-patient department. The objectives were: To determine glycaemic control in the study population and compare differences between age, sex and racial groups , and determine the RBG cut-off with the best sensitivity and specificity for predicting poor glycaemic control (HbA1c>7.0% ) as well as the predictive value, likelihood ratio and pre/post-test odds and probability at this cut off. Methods: A retrospective analysis of existing hospital data and the HbA1c tests requested from the NHLS by Karl Bremer Hospital over the 2011 year period. The data was analysed by means of a receiver operating characteristic (ROC) curve analysis to determine the value of RBG with the best combination of sensitivity and specificity to predict poor control of diabetes. A p-value of < 0.05 was assumed to represent statistical significance and 95% confidence intervals were used to describe the estimation of unknown parameters. HbA1c level of < = 7% was taken as representing good control and > 7% poor control. Results: Data was obtained on 349 diabetic patients of whom 203 (58.2%) were female and 146 (41.8%) male. This study population had a mean age of 54.7 years, mean RBG of 13.0mmol/l and mean HBA1c of 9.4%. The total number of black patients was 79 (23%), coloured patients 147 (42%) and white patients 122 (35) % and their mean RBG were 15.4 mmol/l, 12.8 mmol/l and 11.9 mol/l respectively. There was a statistically significant correlation between increasing RBG and increasing HbA1c (p< 0.01). The best value obtained on the ROC curve was an RBG of 9.8 mmol/l, which had a sensitivity of 77% and a specificity of 75%, positive predictive value of 0.88, positive likelihood ratio 3.08 and post-test probability of 88.2% for predicting an HbA1c above 7%. Conclusion: It was concluded that a moderate correlation exists between RBG and HbA1c in this population of diabetic patients. .The best RBG for determining poor control, defined as a HbA1c>7.0%, was found to be 9.8mmol/l and this RBG had a sensitivity of 77% , specificity of 75% and positive predictive value of 88%. Significant differences were found in pre- and post -test probability for different racial groups. Point of care testing using this level of RBG for clinical decision making will inappropriately categorise 23% of patients in this population and therefore introducing point of care testing for HbA1c is recommended.