Hemoglobin A1c for the diagnosis of diabetes: To replace or to guide oral glucose tolerance tests?
Aims/Introduction:  To evaluate if hemoglobin A1c (A1C) can replace the use of the oral glucose tolerance test (OGTT) to diagnose diabetes in Chinese patients.


METHODS
Subjects without pre-existing diabetes were included in this community-based study. Each participant received a 75-g OGTT and A1C tests.


RESULTS
A total of 1362 subjects, 512 men and 850 women, aged 18-88 years, were enrolled. The prevalence of diabetes was 7.4 and 7.3% by OGTT and by A1C ≥ 6.5% criteria, respectively. The optimal A1C cut-off for diabetes defined by OGTT was 6.1%. The performance of A1C ≥ 6.1% to find diabetes by OGTT was poor, with a kappa 0.50, sensitivity 80% and specificity 91%. Using current criteria of fasting plasma glucose (FPG) < 5.56 mmol/L to exclude and ≥7 mmol/L to diagnose diabetes (FPG criterion), the sensitivity, specificity and OGTT required were 77.2, 100 and 13.5%, respectively. Using A1C < 5.9% to exclude and ≥7.0% to diagnose diabetes (A1C criterion), the sensitivity, specificity and OGTT required were 89.1, 99.8 and 26.5%, respectively. However, using FPG < 5.56 mmol/L and A1C < 6.1% to exclude, and A1C ≥ 7.0% to diagnose diabetes (A1C plus FPG criterion), the sensitivity, specificity and OGTT required were 85.2, 100 and 18.9%, respectively.


CONCLUSIONS
To screen for diabetes, the A1C criterion is more sensitive than the FPG criterion, with more OGTT needed. The A1C plus FPG criterion reduced the number of OGTT needed with acceptable sensitivity. A1C can guide, but cannot replace, OGTT to diagnose diabetes. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2011.00181.x, 2011).
Department of Internal Medicine, National Taiwan University Hospital ; Graduate Institute of Clinical Medicine, Medical College, National Taiwan University.
Hung-Yuan
HY
Li
Division of Endocrinology, Department of Internal Medicine, Cardinal Tien Hospital, Medical School, Catholic Fu Jen University.
Wen-Ya
WY
Ma
Chia Nan University of Pharmacy and Science, Tainan.
Jung-Nan
JN
Wei
Department of Internal Medicine, National Taiwan University Hospital ; Graduate Institute of Clinical Medicine, Medical College, National Taiwan University.
Mao-Shin
MS
Lin
Department of Internal Medicine, National Taiwan University Hospital ; Graduate Institute of Clinical Medicine, Medical College, National Taiwan University.
Shyang-Rong
SR
Shih
Department of Internal Medicine.
Chi Sheng
CS
Hung
Division of Clinical Pathology, National Taiwan University Hospital Yun-Lin Branch, Yun-Lin, Taiwan.
Cyue-Huei
CH
Hua
Department of Internal Medicine, National Taiwan University Hospital ; Graduate Institute of Clinical Medicine, Medical College, National Taiwan University ; Graduate Institute of Preventive Medicine, National Taiwan University School of Public Health, Taipei.
Lee-Ming
LM
Chuang
Diagnosis; Hemoglobin A1c; Oral glucose tolerance test