South Asians also developed pre-diabetes an average of six years earlier than white Europeans. But regardless of ethnicity, baseline two-hour glucose was found to be the best way of predicting progression.
The analysis of 3,515 patients aged 40 to 75 years showed that 588 (16.7 per cent) had pre-diabetes according to an oral glucose tolerance test (OGTT).
When the OGTTs were repeated in 239 of these patients 12 months later, 11.9 per cent of south Asians with pre-diabetes were found to have developed type-two diabetes, compared with 5.2 per cent of white Europeans.
A further 48.9 per cent of south Asians and 58 per cent of white Europeans still had pre-diabetes at the re-screen. However, 36.9 per cent and 36.6 per cent, respectively, had normal glucose levels.
In south Asian patients, only baseline two-hour glucose was associated with progression to type-two diabetes.
In white Europeans HbA1c was also a factor.
Leicester GP Dr Kamlesh Khunti, who presented the research, said two-hour glucose at baseline was the best predictor of progression in both ethnic groups and could form the basis of an intervention tool among those at high risk of developing type-two diabetes.