Diabet. Med. 27, 762–769 (2010)
Aims There are calls to simplify the diagnosis of Type 2 diabetes mellitus (T2DM) to reduce the burden of undiagnosed disease. Glycated haemoglobin (HbA1c) is therefore being considered as a preferred diagnostic tool to replace the need for an oral glucose tolerance test (OGTT), considered by many as cumbersome and inconvenient. The aim of this study was to examine the potential impact of the preferred use of HbA1c as a diagnostic tool on the prevalence and phenotype of T2DM.
Methods Analysis of the Leicester Ethnic Atherosclerosis and Diabetes Risk (LEADER) cohort for previously undiagnosed individuals between 40 and 75 years of age who had OGTT, repeated if within the diabetes range, and HbA1c results. We compared the prevalence and phenotype of subjects with T2DM based on either HbA1c≥6.5% or OGTT using 1999 World Health Organization criteria.
Results From the total population of 8696, we detected 291 (3.3%) with T2DM from using an OGTT, and 502 (5.8%) had HbA1c≥6.5%. Of those diagnosed with T2DM by OGTT, 93 (1.2%) had HbA1c <6.5% and therefore would not have been classified as having T2DM using proposed criteria. Using HbA1c criteria resulted in 304 (3.5%) additional cases of T2DM, approximately doubling the prevalence. Of these 304 additional people, 172 (56.7%) had impaired glucose tolerance/impaired fasting glycaemia according to 1999 World Health Organization criteria. Using HbA1c criteria there was an increase of 2.2- and 1.4-fold in south Asians and white Europeans detected, respectively.
Conclusions Within this multi-ethnic cohort, we found that introducing HbA1c≥6.5% as the preferred diagnostic test to diagnose T2DM significantly increased numbers detected with T2DM; however, some people were no longer detected as having T2DM.