Aims To establish the frequency of detection of previously undiagnosed diabetes mellitus as a result of detection of an increased glycated fraction of haemoglobin during high performance liquid chromatography (HPLC) for haemoglobinopathy diagnosis.

Methods A prospective study was carried out over a 3-month period. During that period a total of 2094 patient samples were received for haemoglobinopathy investigation and were included in the study.

Results Fifty samples were found to have an apparent increase in the glycated haemoglobin fraction and of these 38 were found to be from patients with known diabetes. Previously undiagnosed diabetes was discovered in 11 patients and it is likely that the twelfth patient also had diabetes.

Conclusions The detection of evidence of undiagnosed diabetes during HPLC haemoglobinopathy investigations is not rare, there being four cases per month in this study. This incidental observation should be reported to clinical staff.