Glycated Haemoglobin A1c as a Diagnostic Tool in Diabetes and Prediabetes
Issue: 2/2011
Author: Tsvetalina Tankova, Nevena Chakarova, Lilya Dakovska, Iliana Atanassova
Abstract:
During recent years there is an increasingly recognized need to develop strategies for diabetes screening and diagnosis that will allow effective early disease detection. The aim of the present study is to assess HbA1c in subjects with different glucose tolerance – normal glucose tolerance (NGT), impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and newlydiagnosed diabetes (NDD) and to evaluate the potential role of HbA1c as a diagnostic tool for undetected diabetes and prediabetes.
A total of 2134 subjects (899 males and 1235 females), of mean age 50,3±13,9 years and mean BMI 29,5±6,2 kg/m2 were included in the study. According to glucose tolerance they were divided into 4 groups – 1198 with NGT, 313 with IFG, 241 with IGT and 382 with NDD. All participants underwent a standard OGTT; categories of glucose tolerance were defined according to 2006 WHO criteria. Fasting and 2-hour plasma glucose was measured by a hexokinase enzyme method. HbA1c was measured by an immunoturbidimetric method. Statistical analysis of data was performed by SPSS 17.0. Receiver operating characteristic (ROC) curve analysis was used to examine the sensitivity and specificity of HbA1c for detecting diabetes and prediabetes.
HbA1c was significantly higher in all groups with altered glucose tolerance – 5,72±0,61% in IFG, 5,84±0,63% in IGT and 7,5±1,69% in NDD as compared to NGT – 5,23±0,65% (p<0,0001). There was significant difference in HbA1c between the two prediabetic states (p=0,02); HbA1c of both groups being significantly lower as compared to NDD (p<0,0001). Significant positive correlation was established between HbA1c and both fasting (r=0,78, p<0,001) and 2- hour plasma glucose (r=0,76, p<0,001). ROC analysis demonstrated strong correlation between HbA1c and undiagnosed diabetes, with an area under the ROC curve (AUC-ROC) of 0,958 (95% CI: 0,946-0,970), as well as with undiagnosed prediabetes – AUC-ROC of 0,729 (95% CI: 0,702-0,755). The optimal cut-off level of HbA1c for diagnosis of diabetes was 6,1% with a sensitivity of 86% and specificity of 92%. The optimal cut-off level of HbA1c for undiagnosed prediabetes (IFG and IGT) appeared to be 5,5% with a sensitivity of 71% and specificity of 64%.
In conclusion, HbA1c appears to be a useful, convenient and reliable tool for identifying subjects with prediabetes and diabetes and it should be considered in the development of diagnostic strategies.
Keywords: HbA1c, diagnosis, diabetes, prediabetes.
