Systematic analysis with a five-hour OGTT of 340 subjects representative of people likely to be examined in a center specialized in diabetes detection was performed by multiple discriminant analysis, which provides indices of discrimination for different sets of blood glucose (BG) values. The relative sensitivity and the relative specificity of six different diagnostic methods: Fajans and Conn, Wilkerson, WHO, British Diabetic Association, UGDP, and European Study Group of Diabetes Epidemiology were computed, giving a quantitative determination for the degree of discrepancy in the definition of diabetes: only 48 per cent of the subjects are classified in the same way by any of the diagnostic criteria. The time(s) of sampling and the index or indices of OGTT which are the most efficient in screening diabetes were estimated from homogeneous groups of subjects universally recognized as nondiabetic (URND) or as diabetic (URD) according to the different diagnostic methods. Better discriminating power (DP) between URD and URND compared with the maximum DP as measured by D2 of Mahalanobis from the seven BG values of the OGTT is given by the two-hour (70.2 per cent) than by the one-hour (49.5 per cent) BG value when a single value is used; the one-two-hour BG value is the best set of two times (80.7 per cent). The different indices now in use for the classification of the OGTT have been found less effective than the weighted sum of one-two-hour BG values. The difficulty in obtaining highly specific diagnostic tests is discussed in relation to the consequences on a partly automated screening in large populations.

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