CGM for insulinoma screening: a prospective and observational case-control study.

Insulin release index (IRI) based on 72-h fasting test has been used for the definitive diagnosis of insulinoma; however, hospitalization and subsequent costs contribute to the disadvantage of IRI. Therefore, a simple and cost-effective screening procedure for the diagnosis of insulinoma for outpatients are crucially needed. Continuous glucose monitoring (CGM) has been widely used for monitoring high level of glucose in diabetic patients. The aim of the study is to determine the potential contribution or implementation of CGM in the screening of the insulinoma. We performed a single-center prospective study with the demographics and laboratory data including 28 patients with the pathological diagnosis of insulinoma and 25 patients with functional hypoglycemia as control group. The analysis showed that areas under the receiver operating characteristic (ROC) curve of coefficient of variation (CV) was 0.914. The CV cutoff point was 19% with the Youden 62.1%, the corresponding sensitivity and specificity were 82.1 and 80%, respectively. In patients with CV greater than the median, more than 60% of insulinomas were located in the head of the pancreas; most Ki-67 values were more than 2% and when compared with the group with CV smaller than the median, the average tumor size was 2.7 times larger. In conclusion, CGM can be used as a valuable tool in not only monitoring high glucose levels in diabetic patients but also identifying the etiology of insulinoma. CV greater than 19% can be highly effective for the screening of insulinoma in outpatients.