Elizabeth Goyder, John J Featherstone
Background: Fourteen percent of adults over 60 years may have type two diabetes mellitus, with up to half of these undiagnosed. Screening of high-risk populations is recommended by policymakers, but there is no direct evidence of benefit for those screened. Although abdominal obesity is a recognized risk factor for diabetes, there is controversy regarding its best measure, and its usefulness as a screening measurement is not widely evaluated. Aim: To evaluate the relative performance of waist circumference, body mass index, age and random capillary blood glucose as measurements within a screening programme, in terms of the number of screening tests and diagnostic tests carried out (costs), and the number of cases diagnosed (outcome). Methods: Using national pilot data the study population (n = 4343) comprising those eligible for screening (age _40 years, body mass index _25 kg/m2, no pre-existing diabetes or cardiovascular disease) is described. Threshold analyses by the key variables are displayed in terms of numbers needed to screen and test per new case. Receiver operating characteristic curve analysis evaluates their usefulness as screening measurements in this context. Results: The area under the curve for waist circumference is 63.4% compared to 61.5% for body mass index and 60.9% for age; with overlapping confidence intervals. Random capillary blood glucose of levels over 6 mmol/l have a significantly greater area under the curve of 73.2%. This difference becomes insignificant when analysed by sex. Discussion: The theoretical advantage of waist circumference over body mass index as a screening measurement is not demonstrated in a real-life screening programme. If, in addition to age, another measure to select and define a high-risk population for screening is required, body mass index is recommended. Direct blood glucose measurement remains the most effective screening tool.
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