title: Can HbA1c replace OGTT for the diagnosis of diabetes mellitus among Chinese patients with impaired fasting glucose?
abstract: BACKGROUND
  HbA1c ≥ 6.5% has been recommended as a diagnostic criterion for the detection of diabetes mellitus (DM) since 2010 because of its convenience, stability and significant correlation with diabetic complications. Nevertheless, the accuracy of HbA1c compared to glucose-based diagnostic criteria varies among subjects of different ethnicity and risk profile.
  
  
  OBJECTIVE
  This study aimed to evaluate the accuracy of HbA1c for diagnosing DM compared to the diagnosis by oral glucose tolerance test (OGTT) and the optimal HbA1c level to diagnose DM in primary care Chinese patients with impaired fasting glucose (IFG).
  
  
  METHODS
  A cross-sectional study was carried out in three public primary care clinics in Hong Kong. About 1128 Chinese adults with IFG (i.e. FG level between 5.6 and 6.9 mmol/l in the past 18 months) were recruited to receive paired OGTT and HbA1c tests. Sensitivities and specificities of HbA1c at different threshold levels for predicting DM compared to the diagnosis by OGTT were evaluated. A receiver operating characteristic (ROC) curve was used to determine the optimal cut-off level.
  
  
  RESULTS
  Among the 1128 subjects (mean age 64.2±8.9 year, 48.8% male), 229 (20.3%) were diagnosed to have DM by OGTT. The sensitivity and specificity of HbA1c ≥6.5% were 33.2% and 93.5%, respectively, for predicting DM diagnosed by OGTT. The area under the ROC curve was 0.770, indicating HbA1c had fair discriminatory power. The optimal cut-off threshold of HbA1c was 6.3% for discriminating DM from non-DM, with sensitivity and specificity of 56.3% and 85.5%, respectively. HbA1c ≥ 5.6% has the highest sensitivity and negative predictive value of 96.1% and 94.5%, respectively.
  
  
  CONCLUSIONS
  HbA1c ≥ 6.5% is highly specific in identifying people with DM, but it may miss the majority (66.8%) of the DM cases. An HbA1c threshold of <5.6% is more appropriate to be used for the exclusion of DM. OGTT should be performed for the confirmation of DM among Chinese patients with IFG who have an HbA1c between 5.6% and 6.4%.
authors.affiliation: Department of Family Medicine and Primary Care, The University of Hong Kong, 3/F, Ap Lei Chau Clinic, No. 161 Main Street, Ap Lei Chau and ytyu@hku.hk.
authors.forename: Esther Y T
authors.initials: EY
authors.lastname: Yu
authors.affiliation: Department of Family Medicine and Primary Care, The University of Hong Kong, 3/F, Ap Lei Chau Clinic, No. 161 Main Street, Ap Lei Chau and.
authors.forename: Carlos K H
authors.initials: CK
authors.lastname: Wong
authors.affiliation: Department of Family Medicine and Primary Care, The University of Hong Kong, 3/F, Ap Lei Chau Clinic, No. 161 Main Street, Ap Lei Chau and.
authors.forename: S Y
authors.initials: SY
authors.lastname: Ho
authors.affiliation: Division of Family Medicine and Primary Healthcare, The Jockey Club School of Public Health and Primary Care, The Chinese University of Hong Kong, 2/F, School of Public Health, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.
authors.forename: Samuel Y S
authors.initials: SY
authors.lastname: Wong
authors.affiliation: Department of Family Medicine and Primary Care, The University of Hong Kong, 3/F, Ap Lei Chau Clinic, No. 161 Main Street, Ap Lei Chau and.
authors.forename: Cindy L K
authors.initials: CL
authors.lastname: Lam
mesh_terms: D000368:Aged; D001786:Blood Glucose / Q000378:metabolism; D003430:Cross-Sectional Studies; D003920:Diabetes Mellitus / Q000097:blood / Q000175:diagnosis*; D005215:Fasting / Q000097:blood*; D005260:Female; D018149:Glucose Intolerance; D005951:Glucose Tolerance Test / Q000379:methods*; D006442:Glycated Hemoglobin / Q000032:analysis*; D006723:Hong Kong; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity
chemical_list: D001786:Blood Glucose; D006442:Glycated Hemoglobin
keywords: Chinese; HbA1c; OGTT.; diabetes mellitus; diagnosis; impaired fasting glucose