Objective: To assess the utility of glycated haemoglobin (HbA1c) level as an automated screening test for undiagnosed diabetes among hospitalised patients and to estimate the prevalence of undiagnosed diabetes among hospitalised patients. Design, participants and setting: A 3-month prospective study of all adult patients admitted to a tertiary hospital. An HbA1c test was automatically undertaken on admission for all patients with a random plasma glucose (RPG) level ≥ 5.5 mmol/L. Demographic, admission and biochemical data were obtained from hospital databases.