UNIVARIATE AND BIVARIATE ADMIXTURE ANALYSES OF SERUM GLUCOSE AND GLYCATED HEMOGLOBIN DISTRIBUTIONS IN A JERUSALEM POPULATION-SAMPLE

Univariate and bivariate analyses of fasting glucose and glycated hemo globin (HbA(1c)) levels and of glucose levels 2 hours after an oral gl ucose load test were performed in a random sample of the Jewish popula tion of Jerusalem, aged 25-64 years. Using Intransformed data, we foun d that a mixture of two distributions fits the glucose data significan tly better than a single distribution in the age groups 25-44 and 45-5 4 years. The fasting glucose results indicate that 1.1% of subjects ag ed 25-44 and 3.7% of subjects aged 45-64 without known diabetes come f rom an upper distribution with mean values of 154 mg/dl and 224 mg/dl, respectively. Estimates from the analysis of glucose levels after a l oad test indicate that an additional 2.1% of younger subjects and 3.8% of older subjects belong to a minor distribution with a high mean glu cose value. The frequency distribution of HbA(1c) is also bimodal in a ll age groups. Yet the bimodality indicates that only 0.1% and 2.3% of subjects in the two age groups, respectively, come from minor distrib utions with mean levels of 13.0-15.7%, compared with HbA(1c) values of 5.0% and 5.3% for the main distributions, Using glucose levels, we fo und that specificity rates are consistently greater than 99%, whereas sensitivity rates vary with age. The use of cutoff points suggested by the National Diabetes Data Group (140 mg/dl for fasting glucose level and 200 mg/dl for glucose level after an oral glucose load test) indi cates a lower sensitivity rate in the younger subjects with a minimal improvement among older subjects. A mixture of bivariate log-normal di stributions fitted to the fasting and 2-hour glucose levels in subject s aged 45-64 indicates a larger proportion (6.3%) belonging to the min or distribution compared with those obtained when a single variable is used, Yet this combined score shows a low specificity rate, No simila r improvement in separating ''normal'' from ''abnormal'' subjects is a chieved when a mixture of bivariate distributions is fitted to the glu cose and HbA(1c) variables. Admixture of glucose and HbA(1c) distribut ions is demonstrated. Bivariate analysis of these distributions does n ot, however, provide better discrimination of putatively abnormal subj ects than univariate analysis.