Clinical implication of fasting and post-challenged plasma glucose in diagnosis of diabetes mellitus

Fasting plasma glucose (FPG) is the preferred test in diagnosis of diabetes mellitus (DM) to 2-h post-challenged plasma glucose (2hPG). There is little information available on the comparison between FPG and 2hPG diagnostic criteria. This study included adult participants (≥18 years old) of the NHANES 2005–2010 with FPG, 2hPG, and BMI measured. Subjects with established DM were excluded. The sensitivity of FPG and 2hPG diagnostic criteria was compared as the main outcome measure. Among 5,782 subjects, 476 subjects (8.23 %) were diagnosed with DM by either FPG, 2hPG, or both criteria. Among the subjects meeting the criterion of FPG, those with 2hPG <200 mg/dL were younger (57 ± 16 vs. 61 ± 15 years old, P < 0.05, mean ± STD) and less obese (30.81 ± 7.89 vs. 32.71 ± 6.68 kg/m², P < 0.05) as compared to those with 2hPG ≥200 mg/dL. Among the subjects meeting the criterion of 2hPG, those with FPG <126 mg/dL were more female (55.41 vs. 39.88 %, P < 0.0002), less obese (29.24 ± 5.83 vs. 32.71 ± 6.68 kg/m², P < 0.000001), lower diastolic blood pressure (67 ± 12 vs. 71 ± 14 mmHg, P < 0.02), and less family history of DM (36.35 vs. 48.47 %, P < 0.02) as compared to those with FPG ≥126 mg/dL. The sensitivity of diagnosis of DM was only 41.37 % for FPG criterion, while it was 66.53 % for 2hPG criterion. Thus, compared to 2hPG criterion, FPG criterion had a lower sensitivity detecting new cases of DM. The use of FPG criterion would more likely result in underdiagnosing DM, especially in female and less obese subjects, as compared to the use of 2hPG criterion.