812 ENDOCRINE PRACTICE Vol 19 No. 5 September/October 2013 Original Article Rinkoo Dalan, MBBS, MRCP(UK), FRCP(Edin), FAMS(Endocrinology) 1,2,3 ; Arul Earnest, PhD, MSc 3 ; Melvin Khee Shing Leow, MBBS, FRCP(Edin), FACE, FACP, PhD 3,4 Submitted for publication December 13, 2012 Accepted for publication March 12, 2013 From the 1 Department of Endocrinology, Tan Tock Seng Hospital, Singapore, 2 Yong Loo Lin School of Medicine, Singapore, 3 Duke-NUS Graduate Medical School, Singapore, and the 4 Brenner Centre for Molecular Medicine, National University of Singapore, Singapore. Address correspondence to Dr. Rinkoo Dalan, Department of Endocrinology, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433. E-mail: rinkoo_dalan@ttsh.com.sg. Published as a Rapid Electronic Article in Press at http://www.endocrine practice.org on May 24, 2013. DOI:10.4158/EP12417.OR To purchase reprints of this article, please visit: www.aace.com/reprints. Copyright © 2013 AACE. ABSTRACT Objective: We aimed to determine the relationship between fasting serum glucose (FSG) concentration and glycated hemoglobin-A1c (HbA1c) in the 3 ethnicities in Singapore after adjustment for demographic and therapeu- tic variables. Methods: Fasting serum glucose (FSG), HbA1c, and serum creatinine levels were simultaneously sampled from 575 patients with diabetes (389 Chinese, 97 Indians, 89 Malays) in this cross-sectional study between January and May 2008, and the results were subjected to multivariate linear regression analysis. Results: We found a signifcant interaction between FSG and ethnicity on HbA1c. The correlation between FSG and HbA1c among Chinese subjects was 0.25 (95% confdence interval [CI]:0.2-0.3) relative to the Malays (0.38, 95% CI: 0.30-0.45) after adjustment for age; gen- der; serum creatinine concentrations; body mass index (BMI); duration of diabetes; use of sulfonylureas, metfor- min, and insulin; and hemoglobin (Hb) and red cell indices (P = .005). Hence, for a given FSG, the predicted HbA1c will be higher in Malays compared to Chinese subjects. We did not observe a statistically signifcant difference between Indians and Malays with respect to the correlation between FSG and HbA1c. Conclusion: We showed a higher correlation between HbA1c and FSG in Malay subjects relative to the Chinese in this cohort. The ethnic variation in the HbA1c–FSG relationship may be related to differences in percentage contribution by the FSG to overall HbA1c among ethnic groups. Future studies using continuous glucose monitor- ing (CGM) to elucidate the relative contributions by FSG and postprandial glucose (PPG) to the daily blood glucose profle and the overall HbA1c by ethnicity are required. (Endocr Pract. 2013;19:812-817) Abbreviations BMI = body mass index; DCCT = Diabetes Control and Complications Trial; FSG = fasting serum glucose; Hb = hemoglobin; HbA1c = glycated hemoglobin-A1c; OGTT = oral glucose tolerance test; PPG = postpran- dial glucose INTRODUCTION Glycated hemoglobin-A1c (HbA1c) is an areal func- tion of the glucose-time curve correlating with mean plasma glucose and remains an important indicator of long-term glycemic control in diabetes mellitus (1). It is well established that HbA1c refects contributions from both basal (fasting) and postprandial hyperglycemia, and recently it has been seen that regardless of treatment with oral hypoglycemic agents and basal or prandial insulin, fasting serum glucose (FSG) contributes to at least one- third of total glycemia (patients with basal insulin) and two- thirds with other treatment options in patients with HbA1c >7.0% (2). In the Singapore National Health Survey 2010, it was seen that Malay patients with diabetes had the high- est proportion (47.6%) of cases with poor glycemic control as defned as HbA1c >7.0% compared to Chinese (24.9%) and Indians (37.9%) (3). In a prospective cohort study