The WHO is revising global advice on diabetes diagnosis.
Its current guidelines are used by Diabetes UK and NICE.
The advice will include an update on diabetes classification and the use of glucose intolerance, HbA1c and risk scores in diagnosing, screening and predicting diabetes.
But a WHO spokesman said it would 'not include ethnic-specific thresholds for any of the measures'.
Professor Eric Kilpatrick, chemical pathology consultant at Hull Royal Infirmary, has raised concerns about basing diabetes diagnosis on HbA1c.
He said research showed HbA1c levels are raised in Afro-Caribbean, Asian and elderly people.
'What we do not yet know is how appropriate it will be to identify a higher proportion of elderly and ethnic minority individuals if a single diagnostic HbA1c threshold for diabetes comes into use,' he said.
Simon O'Neill, director of care, information and advocacy for Diabetes UK, said the charity expected the WHO to back HbA1c as a screening method, with a single cut-off value.
'As with current diagnostic criteria, clinicians will need to use their clinical judgment to use varying screening criteria for different groups,' he said.
'People of south Asian descent should be tested at an earlier age and lower BMI than people of a Caucasian background.'
RCGP clinical lead for diabetes Dr Brian Karet said that using HbA1c alone to screen for diabetes would increase diagnoses by 10-15 per cent.
Many patients with impaired glucose tolerance will not go on to develop diabetes, he said.
'I wonder if it's going to medicalise whole sections of the population,' he said. 'Personally, I'm not in favour of it.'