Combined Use of a Fasting Plasma Glucose Concentration and HbA_1c or Fructosamine Predicts the Likelihood of Having Diabetes in High-Risk Subjects

To assess the validity of using fasting plasma glucose (FPG) concentrations in conjunction with HbA_1c or fructosamine for the screening of diabetes in high-risk individuals.

In this study 2,877 Hong Kong Chinese (565 [19.6%] men; 2,312 [80.4%] women) with various risk factors for glucose intolerance underwent a 75-g oral glucose tolerance test (OGTT) for screening of diabetes. The risk factors included a family history positive for diabetes, a history of gestational diabetes or impaired glucose tolerance, and obesity.

Using World Health Organization (WHO) criteria, 1,593 (55.4%) had normal glucose tolerance, 657 (22.8%) had impaired glucose tolerance, and 627 (21.8%) had diabetes. When the 1997 American Diabetes Association (ADA) criteria were applied, 394 (13.7%) had diabetes with an FPG ≥ 7.0 mmol/l. Using multiple receiver operating characteristic curve analysis, the paired values of an FPG of 5.6 mmol/l and a HbA_1c of 5.5% gave an optimal sensitivity of 83.8% and specificity of 83.6% to predict a 2-h plasma glucose (PG) ≥ 11.1 mmol/l. Likewise, the paired values of an FPG of 5.4 mmol/l and a fructosamine level of 235 mumol/l (n = 2,408) gave an optimal sensitivity of 81.5% and specificity of 83.2%. An FPG ≥ 5.6 mmol/l and an HbA_1c ≥ 5.5% was 5.4-fold more likely to occur in diabetic subjects (based on the WHO criteria) compared with nondiabetic subjects. For paired parameters less than these values, the likelihood ratio of this occurring in diabetic subjects was only 0.11. Similarly, an FPG ≥ 5.4 mmol/l and a fructosamine ≥ 235 μmol/l was fivefold more likely to occur in diabetic subjects than in nondiabetic subjects, with both parameters less than these values having a likelihood ratio of 0.04. Using these paired values as initial screening tests, only subjects who had an FPG ≥ 5.6 mmol/l and < 7.8 mmol/l and a fructosamine ≥235 μmol/1 (n = 526) required OGTT to confirm diabetes, meaning that 78.2% [(2,408 – 526)/2,408] of the OGTTs could have been saved. Based on the 1997 ADA criterion of an FPG cutoff value of 7.0 mmol/1, the corresponding numbers of OGTTs to be saved were 82.6% and 85.5%, respectively.

The paired values of FPG and HbA_1c or FPG and fructosamine helped to identify potentially diabetic subjects, the diagnosis of which could be further confirmed by the 75-g OGTT. Using this approach ∼ 80% of OGTTs could have been saved, depending on the diagnostic cutoff value of FPG.