Dirk Christensen and colleagues from the University of Copenhagen looked at screen-detected diabetes prevalence. They compared the degree of diagnostic agreement between oral glucose tolerance test (OGTT) criteria and HbA1c-diagnostic criteria.

HbA1c-only tests have been proposed by an international expert panel. If the WHO backs this view, the DoH and Diabetes UK will consider it too.

But Dr Christensen and colleagues' results suggest that, in those of South Asian origin, an HbA1c-based test would miss more than a third of cases that OGTT criteria would pick up.

The researchers argue that a shift to an HbA1c-based diagnosis for diabetes will have substantially different consequences for diabetes prevalence across ethnic groups and populations.

Last month, a leading biochemist warned that using HbA1c alone to screen for type-2 diabetes risked misdiagnosing large numbers of patients. In people of African, Mediterranean or south-east Asian heritage with diabetes, HbA1c can be inaccurate, he pointed out.