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Aims The objectives of the study were to assess the predictive value of baseline HbA1c for incident diabetes among the participants with impaired glucose tolerance in the Indian Diabetes Prevention Programmes 1 and 2. Methods Data at baseline and at 3-year follow-up were analysed in combined cohorts of the Indian Diabetes Prevention Programmes 1 and 2. Within the 3 years, 324 of the 845 participants developed diabetes (World Health Organization criteria). The predictive value of baseline HbA1c for incident diabetes was determined by logistic regression analysis. Results Baseline HbA1c values had heterogenous distribution. The distribution was similar in isolated impaired glucose tolerance or in impaired glucose tolerance in combination with impaired fasting glucose. A progressive increase in diabetes occurred with increasing HbA1c. HbA1c showed the strongest association with incident diabetes in the multiple logistic regression analysis (odds ratio 3.548, P < 0.0001). The cut-off HbA1c of 43 mmol/mol (6.05%) had 67% sensitivity and 60% specificity to predict future diabetes. The diagnostic sensitivity of HbA1c of ≥ 48 mmol/mol (≥ 6.5%) was only 51%, with a specificity of 87%, when compared with the oral glucose tolerance glucose values. Conclusions Baseline HbA1c was highly predictive of future diabetes in Asian Indian subjects with impaired glucose tolerance and nearly 60% of the incidence occurred with values ≥ 42 mmol/mol (≥ 6.0). Diagnostic sensitivity of HbA1c≥ 48 mmol/mol (≥ 6.5%) for new diabetes was only 51% using the oral glucose tolerance test as the standard for comparison.