What is the risk of mortality for people who are screen positive in a diabetes screening programme but who do not have diabetes on biochemical testing? Diabetes screening programmes from a public health perspective.

OBJECTIVES: To assess mortality risk in people classified by the Cambridge risk score (CRS), a previously validated simple screening tool for undiagnosed type 2 diabetes that uses only information routinely available in primary care.
SETTING: Random sample of the general population between 50 and 75 years of age in Hoorn, The Netherlands
METHODS: The results of the CRS were compared with the gold standard for diabetes, the oral glucose tolerance test (OGTT) results classified according to the World Health Organisation (WHO) 1999 diagnostic criteria. Cox's proportional hazards regression was used to assess the risk of mortality of screen positive and screen negative people.
RESULTS: 154 people out of the total population of 2297 had previously undiagnosed diabetes and 113 (73%) of these would have been detected with the CRS (true positive). However, the CRS identified a much larger group (n=1037) who were positive for the score, but who did not have diabetes on biochemical testing (false positive). Unadjusted risk of mortality was highest in the true positive group (3.40 95% confidence interval (95% CI, 2.15 to 5.38)), intermediate in false positive people (2.62 (2.00 to 3.43)), and lowest in false negative people (1.50 (0.55 to 4.09)) with the true negative group as reference. Adjustment for age and sex resulted in similar risk estimates for all three groups, but mortality risk was significantly increased only in false positive and true positive groups compared with the true negative group.
CONCLUSIONS: People who have a positive risk score are at high risk of mortality whether or not subsequent testing shows them to have diabetes. Direct public health interventions in this high risk population may be appropriate.