Which combination is best for HbA1c, fasting plasma glucose, and 2-h post-challenge glucose for diagnosis of diabetes mellitus

Abstract Background We evaluated reliability among glycated hemoglobin (HbA1c), fasting plasma glucose (FPG), and a 75 g oral glucose tolerance test (75 g OGTT) where 2-h post-challenge glucose level (2hPG) in the diagnosis of diabetes and pre-diabetes to find out which parameter or combination of parameters is useful. Methods All the participants received 75 g OGTT and HbA1c measurements. For FPG, < 110 mg/dL was defined as “normal”, 110 ≤ FPG < 126 mg/dL was defined as “pre-diabetes”, and 126 mg/dL ≤ FPG was defined as “diabetes”. For 2hPG, < 140 mg/dL was defined as “normal”, 140 mg/dL ≤ 2hPG < 200 mg/dL was defined as “pre-diabetes”, and 200 mg/dL ≤ was defined as “diabetes”. For HbA1c, ≤ 6.2% was defined as “normal”, 6.2 < HbA1c < 6.5% was defined as “pre-diabetes”, and 6.5% ≤ was defined as “diabetes”. The prevalence of diabetes and pre-diabetes were estimated based on 7 different combinations as the following: “the combination of either HbA1c or FPG or 2hPG”, “the combination of either HbA1c or 2hPG”, “the combination of either HbA1c or FPG”, “HbA1c alone”, “the combination of either FPG or 2hPG”, “2hPG alone”, and “FPG alone”. Each diagnosed group were then divided into different age groups (40 s, 50 s, 60 s, 70 s, and 80 s) to consider the effect of age on results. Results For diagnosing “diabetes”, “the combination of either HbA1c or 2hPG” was almost as reliable as “the combination of either HbA1c or FPG or 2hPG” throughout all ages except for the 50 s. For diagnosing “pre-diabetes”, “the combination of either HbA1c or 2hPG” was almost as reliable as “the combination of either HbA1c or FPG or 2hPG” throughout all ages. Discussion Combining our results, measurement of HbA1c and 2hPG seems to be recommended for the diagnosis of diabetes and pre-diabetes. This means for an accurate diagnosis of diabetes and pre-diabetes, not only the measurement of HbA1c but also a 75 g OGTT is recommended. Unfortunately, screening by FPG alone is not recommended from this clinical study. Conclusions For accurate diagnosis of diabetes and pre-diabetes, the combination of HbA1c measurement and 75 g OGTT seemed to be a secure concept.