Background The prevalence of type 2 diabetes within the Republic of Ireland is poorly defined, although a recent report suggested 135,000 cases in adults aged 45+, with approximately one-third of these undiagnosed. This study aims to assess the prevalence of undiagnosed and diagnosed diabetes in middle-aged adults and compare features in order to investigate why certain individuals remain undetected.

Methods This was a cross-sectional study involving a random sample of 2,047 men and women aged 50–69 years. Logistic regression was used to explore socio-economic, metabolic and other health-related feature associations with undiagnosed or diagnosed diabetes. Clinically relevant variables identified in regression analyses were assessed using the receiver operating characteristic curve.

Results The total prevalence of diabetes was 8.5% (95% CI: 7.4%-8.8%); 72 subjects (3.5%) had undiagnosed diabetes (95% CI: 2.8%-4.4%) and 102 subjects (5.0%) had diagnosed diabetes (95% CI: 4.1%-6.0%). Obesity, dyslipidaemia, and having a family diabetes history were positively associated with both undiagnosed and diagnosed type 2 diabetes. Compared with diagnosed subjects, study participants with undiagnosed diabetes were significantly more likely to have low levels of physical activity and were less likely to be on treatment for diabetes-related conditions or to have private medical insurance.

Conclusion A considerable proportion of diabetes cases were undiagnosed (41%), emphasising the need for more effective detection strategies and equitable access to primary healthcare.