Comparison of the Current Diagnostic Criterion of HbA1c with Fasting and 2-Hour Plasma Glucose Concentration

Abstract

To determine the effectiveness of hemoglobin A1c (HbA1c) ≥ 6.5% in diagnosing diabetes compared to fasting plasma glucose (FPG) ≥ 126 mg/dL and 2-hour plasma glucose (2hPG) ≥ 200 mg/dL in a previously undiagnosed diabetic cohort, we included 5,764 adult subjects without established diabetes for whom HbA1c, FPG, 2hPG, and BMI measurements were collected. Compared to the FPG criterion, the sensitivity of HbA1c ≥ 6.5% was only 43.3% (106 subjects). Compared to the 2hPG criterion, the sensitivity of HbA1c ≥ 6.5% was only 28.1% (110 subjects). Patients who were diabetic using 2hPG criterion but had HbA1c < 6.5% were more likely to be older (64 ± 15 versus 60 ± 15 years old, P = 0.01, mean ± STD), female (53.2% versus 38.2%, P = 0.008), leaner (29.7 ± 6.1 versus 33.0 ± 6.6 kg/m2, P = 0.000005), and less likely to be current smokers (18.1% versus 29.1%, P = 0.02) as compared to those with HbA1c ≥ 6.5%. The diagnostic agreement in the clinical setting revealed the current HbA1c ≥ 6.5% is less likely to detect diabetes than those defined by FPG and 2hPG. HbA1c ≥ 6.5% detects less than 50% of diabetic patients defined by FPG and less than 30% of diabetic patients defined by 2hPG. When the diagnosis of diabetes is in doubt by HbA1c, FPG and/or 2hPG should be obtained.

Clinical Implications of Using Post-Challenge Plasma Glucose Levels for Early Diagnosis of Type 2 Diabetes Mellitus in Older Individuals

“…Elevated HbA1c levels in diabetic patients were first reported in 1969 [ 31 ] and were shown to indicate aggravated glucose levels over a 3-month period [ 32 ]. Since the HbA1c level was included as a diagnostic criterion by the American Diabetes Association in 2010, many researchers have explored its diagnostic efficacy and have examined the optimal cutoff values [ 10 33 34 35 36 ]. These studies suggested that the HbA1c level was of low sensitivity when used to screen for diabetes, and the authors concluded that the cutoff values had to be reduced to increase sensitivity.…”

Definition, Classification and Diagnosis of Diabetes, Prediabetes and Metabolic Syndrome

“…In a Canadian context, A1C may identify more people as having diabetes than FPG (27). However, other studies suggest A1C may not identify as many people as having diabetes compared to FPG or 2hPG (28).…”

The simultaneous assessment of glycosylated hemoglobin, fasting plasma glucose and oral glucose tolerance test does not improve the detection of type 2 diabetes mellitus in Colombian adults

“…In addition, significant differences in HbA1c cut-off points for DM2 according to ethnicity, age, sex, and population prevalence of diabetes were noted [ 7 , 8 ]. In US adults Karnchanasorn et al [ 9 ] reported also found that HbA1c ≥ 6.5% had a low diagnostic capacity relative to both FPG and OGTT, suggesting that a substantial number of cases of DM2 would be missed using this criterion. This data, from over 5000 participants of the NHANES 2005–2010 showed that of 392 subjects who met ADA criterion for DM2 according to OGTT only 28.1% were identified by HbA1c, while of 245 subjects who met FPG cut points only 43.3% were also diagnosed by HbA1c.…”

“…Although the risk factors [ 7 ] and the criteria for the diagnosis of DM2 are well defined [ 5 , 6 ], there is ongoing debate as to whether these criteria are universally associated with the future risk of vascular complications [ 8 ]. Furthermore, a recent study found that based on the current cut-points, HbA1c, had a poor capacity to detect DM2 in US adults relative to OGTT and FPG [ 9 ]. Given the expense of conducting all three tests and the fact that in Colombia HbA1c is the most expensive of these, we aimed to determine the capacity of FPG, OGTT and HbA1c to detect DM2 in Colombian adults, and if their simultaneous assessment increases the diagnosis of DM2 according to the criteria of the Colombian guidelines for diabetes and the American Diabetes Association (ADA) [ 5 , 6 ].…”