Objectives: To assess the prevalence of undiagnosed diabetes, impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) in patients over the age of 40 years attending their general practitioner (GP) in Ireland, through opportunistic screening, using a three-step screening tool involving self-determined high-risk groups, random venous plasma glucose (RVPG) measurement and oral glucose tolerance tests.
Design: In participating general practices, 100 consecutive patients > 40 years, completed a screening questionnaire relating to diabetes-related symptoms and risk factors. Patients with previously diagnosed diabetes were not excluded from the study and the screening instrument included a question about known diabetes. Patients without known diabetes mellitus (DM) and with at least two risk factors and/or symptoms underwent a RVPG test. Those with an RVPG above 5.5 mmol/l underwent an oral glucose tolerance test.
Results: Forty-one practices returned 3821 questionnaires. The prevalence of Type 2 diabetes mellitus in the study population was 9.2% (353), of whom 23.5% (83) were previously undiagnosed. DM was detected on the basis of an RVPG >11.1 mmol/l in 0.8% (32) of the studied population. DM was detected on the basis of the oral glucose tolerance test in 1.3% (51) of the population. One per cent (39) had a fasting plasma glucose (FPG) > or = 7.0 mmol/l, 0.6% (24) had a 2-h >11.0 mmol/l and 0.3% (12) had both. Diabetes would not have been detected in 12 people had the 2-h test been omitted. The prevalence rate for IFG and/or IGT was 3.9% (148). Of the 103 patients with IGT, 83 (81%) would have been missed had the GTT been omitted.
Conclusion: Opportunistic diabetes screening in general practice using a screening questionnaire followed by RVPG testing and GTT for those above 5.5 mmol/l is feasible, with a high participation rate. The use of GTTs rather than fasting glucose testing alone improves patient identification, in particular those with IGT who are at higher cardiovascular risk.