To the Editor: Diabetes is a leading cause of morbidity and mortality in Australia, with 50% of cases remaining undiagnosed.1 Consequently, the Australian National Diabetes Strategy has early detection of diabetes as a key priority.2 We undertook a study to determine the prevalence of abnormal glucose metabolism (impaired fasting glycaemia [IFG] and diabetes) in patients presenting in the fasted state for endoscopy or colonoscopy at a metropolitan teaching hospital. We used the definitions of abnormal glucose metabolism outlined by the World Health Organization in 19993 and published in a position statement in the Journal in April 1999.4

Two hundred and twenty-four patients gave informed consent and participated in the study, comprising 126 men and 98 women. Mean age (SD) was 75.1 years (6.9) for men and 60.9 years (17.6) for women. Twenty-four participants (11%) had known diabetes. The remaining 200 patients had fasting venous plasma glucose levels determined (Box). Patients with abnormal glucose metabolism (fasting plasma glucose level > 6.1 mmol/L) were offered further testing with a 2-hour oral glucose tolerance test (OGTT) after a 75 g glucose load. Nine patients initially classified with IFG had diabetes based on OGTT results. No patient classified with diabetes on initial testing was subsequently classified as not having diabetes by the OGTT. The overall prevalence of undiagnosed diabetes was 7% (15 patients).

We demonstrated a high prevalence of abnormal glucose metabolism in a group of predominantly elderly patients presenting for gastroenterological procedures. Furthermore, subsequent investigation of these patients revealed that a substantial proportion who were classified with IFG on initial screening were classified with diabetes based on 2-hour OGTT results, highlighting the importance of this test in diagnosing diabetes.

It is likely that we underestimated the prevalence of abnormal glucose metabolism, as OGTT was not performed in all patients. This is supported by results of the AusDiab study that revealed a high prevalence of abnormal glucose metabolism in older patients — 37% of those aged 55–64 years, 47% of those 65–74 years, and 53% of those 75 years and over.1 National Health and Medical Research Council guidelines suggest that all patients with a fasting plasma glucose level of 5.5–6.9 mmol/L be referred for OGTT.5 Based on this suggestion, an additional 28 patients in our study group would have had an OGTT.

Measurement of fasting venous plasma glucose level is safe, relatively simple and inexpensive. Patient presentations in the fasted state for investigations and procedures provide an ideal opportunity for screening with this test. Patients with abnormal results should be referred for further testing with repeat fasting glucose determination or OGTT. This process may be facilitated by involving patients' general practitioners.

Competing interests: None identified.