The natural history of impaired carbohydrate metabolism has not been established although the importance of identifying patients with abnormally high blood glucose levels has been highlighted internationally.This survey quantifies the direct cost of applying relatively low thresholds for screening targeted patients within the context of primary care in the UK National Health Service. Patients in one practice ‘at-risk’ of diabetes mellitus and with a random blood glucose of 5.5 mmol/l or greaterwere offered a fasting blood glucose, and oral glucose tolerance test if results were inconclusive. Data for all 306 patients with a random blood glucose at or above 5.5 mmol/l from Jan 2002 to April 2003 were available for analysis. In this cohort, with nearly 41% of cases having abnormal blood glucose levels, a policy of selecting a random blood glucose of 6 mmol/l or greater for initiating further screening tests would have resulted in a failure to identify four patients with impaired carbohydrate metabolism. Of these four patients only one required treatment with oral hypoglycaemic agents and that patient presented with symptoms, and therefore testing was clinically indicated. The cost of identifying these four patients was calculated at around £247 each. This excludes the cost and inconvenience to patients with normal results.