Reader Tan Thiam Guan said that his 19-year-old niece requested a HbA1c test at a polyclinic as "we have a history of diabetes in our family".
However, she was told by the doctor that the HbA1c test was not an accurate indicator of diabetes, and that the fasting blood sugar test was preferred.
Since she had not fasted that morning, the doctor refused to authorise any tests.
Mr Tan said: "This is completely opposite to what I have been told. Is the doctor right or wrong?"
Senior Health Correspondent Salma Khalik answered.
In Singapore, HbA1c - which measures sugar in the blood over a three-month period - is used to monitor diabetics to ensure that their condition is under control, and not as a screening tool.
The Ministry of Health (MOH) explains in its guidelines that this is so "until its performance in our multi-ethnic population has been evaluated".
Fasting blood glucose is the preferred screening method as it is supported by strong evidence.
Some countries, however, do accept the use of HbA1c test to screen for diabetes.
The World Health Organisation says the HbA1c test can be used to screen for diabetes, but with conditions such as "stringent quality assurance tests" and "no conditions present that preclude its accurate measurement".
It classifies the evidence on the use of HbA1c to screen for diabetes as "moderate" and the strength of this recommendation as "conditional".
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