The oral glucose tolerance test reveals a high frequency of both impaired glucose tolerance and undiagnosed Type 2 diabetes mellitus in primary hyperparathyroidism

Aims To evaluate the frequency of impaired glucose tolerance (IGT) and undiagnosed diabetes mellitus together with the indices of insulin resistance (IR) in primary hyperparathyroidism (pHPT). Methods Out of 105 consecutive pHPT patients (F/M 78/27, asymptomatic/symptomatic 68/37, age (mean+/-SD) 60.7+/-12.7 years, body mass index 25.2+/-3.8 kg/m(2), ionized calcium (iCa) 1.49+/-0.16 mmol/l, parathormone 200.4+/-233.9pg/ml), 59 without known diabetes mellitus and controls (n=60) underwent an oral glucose tolerance test (OGTT, 75 g os). As indices of IR, homeostasis model assessment (HOMA(IR)) or OGTT data (insulin sensitivity index composite (ISI comp)) were evaluated. Results In pHPT the prevalence of IGT (mean, 95% confidence intervals (CI), 40.7%, 27.8-53.6) was higher than in controls (25.0%, 13.7-36.3, P<0.03). Similarly, the prevalence of undiagnosed diabetes mellitus was higher in pHPT (15.3%, 5.8-24.7) than in controls (5.0%, 0-10.7, P<0.05). Moreover, the prevalence of IGT and undiagnosed diabetes was higher in pHPT than that previously reported in the general population of Northern Italy (8.5% and 3.2%, respectively). The indices showed that insulin resistance was higher in pHPT than in controls: HOMA(IR) (median, 95% CI, 2.6,2.5-3.9 vs. 1.7,1.6-2.5, respectively; P<0.003); ISI comp (3.5, 3.4-4.6 vs. 5.1, 4.9-7.2, respectively; P<0.002). Conclusions Our data in a large and modern day pHPT series, with a preponderance of asymptomatic patients, confirm increased insulin resistance and prevalence of IGT and undiagnosed diabetes.