Diabetes mortality differs between registers due to various disease definitions

INTRODUCTION: We evaluated the impact of including haemo globin A1c (HbA1c) measurements in a regional algorithm for identification of diabetics by comparing the population identified by the regional algorithm with diabetics registered in the National Danish Diabetes Register (NDR) relative to prevalence, co-morbidity and five-year mortality rate. MATERIAL AND METHODS: The regional (County of Vejle) and national diabetes populations were compared per the inclusion date of 31 December 2006 limited to persons residing in four municipalities in the County of Vejle, Denmark. RESULTS: A total of 14,998 diabetics were identified by the regional algorithm, of whom 11,499 (prevalence 4.1%) resided in the four municipalities. The total number of diabetics registered in the NDR was 227,621 in Denmark, of whom 10,976 (prevalence 4.0%) resided in the four municipalities. The regional diabetics (2,802 persons) not identified in the NDR population had a significantly lower mortality rate (57%) than the diabetics (2,279 persons) in the NDR population not identified by the regional algorithm. CONCLUSION: The significantly higher mortality in the NDR population not identified by the regional algorithm may stem from differences between the components of the two algorithms, i.e. frequency of glucose measurements in the NDR versus frequency of HbA1c measurements including elevated values in the regional algorithm. The NDR algorithm, which includes the use of frequency of glucose measurements without a value over the diagnostic threshold, identified about 21% of persons who probably had their glucose measured for other reasons than diabetes.