Fig. 1Flow chart for the selection of study participants. KNHANES, Korea National Health and Nutrition Examination Survey; HbA1c, glycosylated hemoglobin.
Fig. 2Receiver operator characteristic curves for detection of (A) impaired fasting glucose (fasting plasma glucose ≥100 mg/dL) and (B) diabetes mellitus (fasting plasma glucose ≥126 mg/dL) according to glycosylated hemoglobin levels. (A) The area under the curve (AUC) (95% confidence interval [CI]) for impaired fasting glucose was 0.649 (95% CI, 0.648 to 0.650) in the youth group (10 to 19 years of age) and 0.700 (95% CI, 0.699 to 0.701) in the young adult group (20 to 29 years of age) (P<0.001). (B) The AUC (95% CI) for diabetes mellitus was 0.996 (95% CI, 0.996 to 0.996) in the youth group and 0.962 (95% CI, 0.962 to 0.963) in the young adult group (P<0.001).
Table 1Fasting plasma glucose level according to HbA1c category and age group
Age group |
FPG, mg/dL |
HbA1c category |
Total |
<5.7% |
5.7%−6.4% |
≥6.5% |
10–19 yr |
<100 |
3,135 (83.9) |
658 (16.1) |
1 (0.02) |
3,794 (100) |
(93.6) |
(85.1) |
(9.3) |
(91.9) |
100–125 |
214 (66.9) |
110 (32.5) |
3 (0.6) |
327 (100) |
(6.4) |
(14.7) |
(18.5) |
(7.9) |
≥126 |
0 (0) |
3 (27.8) |
5 (72.2) |
8 (100) |
(0) |
(0.4) |
(72.2) |
(0.2) |
Total |
3,349 (82.4) |
771 (17.4) |
9 (0.2) |
4,129 (100) |
(0100) |
(0100) |
(0100) |
(0100) |
20–29 yr |
<100 |
2,702 (90.9) |
276 (9.1) |
0 (0) |
2,978 (100) |
(94.5) |
(80.8) |
(0) |
(92.6) |
100–125 |
149 (71.5) |
54 (27.5) |
2 (1.0) |
205 (100) |
(5.5) |
(18.0) |
(15.1) |
(6.8) |
≥126 |
2 (12.1) |
5 (21.3) |
12 (66.6) |
20 (100) |
(0.1) |
(1.2) |
(84.9) |
(0.6) |
Total |
2,853 (89.1) |
335 (10.4) |
15 (0.5) |
3,203 (100) |
(100) |
(100) |
(100) |
(100) |
Table 2Diagnostic performance of HbA1c according to cutoff values by the present study and ADA/KDA
Criteria |
Age group |
No. (weighted %) |
HbA1c cutoff, % |
Sensitivity, % |
Specificity, % |
PPV, % |
NPV, % |
FPG ≥100 mg/dL |
10−19 yr |
335 (8.1) |
5.6 (present study) |
49.9 |
73.3 |
14.2 |
94.3 |
5.7 (ADA/KDA) |
35.0 |
83.9 |
16.1 |
93.6 |
20−29 yr |
225 (7.4) |
5.5 (present study) |
54.3 |
72.9 |
13.8 |
95.2 |
5.7 (ADA/KDA) |
33.2 |
90.9 |
22.6 |
94.5 |
FPG ≥126 mg/dL |
10−19 yr |
8 (0.2) |
5.9 (present study) |
100 |
95.8 |
5.34 |
100 |
6.5 (ADA/KDA) |
72.2 |
99.9 |
72.2 |
99.9 |
20−29 yr |
20 (0.6) |
5.8 (present study) |
87.9 |
94.6 |
8.8 |
99.9 |
6.5 (ADA/KDA) |
66.6 |
99.9 |
85.0 |
99.8 |
Table 3Cutoff values of glycosylated hemoglobin for prediabetes and diabetes
Country |
Age, yr |
Degree of obesity |
Cutoff value, % |
Reference |
Korea |
50±13 |
NA |
Prediabetes 5.7 |
[30] |
Diabetes 6.1 |
China |
52.4±13.3 |
NA |
Prediabetes 5.6 |
[31] |
Diabetes 6.1 |
Asia & Europe |
NA |
NA |
Diabetes 6.1 |
[32] |
USA |
13.2±2.8 |
Obese |
IGT 5.5 |
[22] |
T2DM 5.8 |
UK |
5–15 |
NA |
IFG 5.4 |
[33] |
Korea |
9.9±3.0 |
Overweight and obese |
IGT 5.8 |
[16] |
Korea |
13.0±2.5 |
Overweight and obese |
Prediabetes 5.8 |
[17] |
Diabetes 6.2 |