Using the Secretion Ratios of Insulin and C-peptide During the 2-h Oral Glucose Tolerance Test to Diagnose Insulinoma

• Published in: Digestive diseases and sciences Vol. 66; no. 5; pp. 1533 - 1539
• Main Authors: Liao, Jing, Ding, Fei, Luo, Wei, Nie, Xin, He, Yong, Li, Guixing
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.05.2021; Springer; Springer Nature B.V
• Subjects: Accuracy; Biochemistry; Dextrose; Diabetes therapy; Gastroenterology; Glucose; Glucose tolerance tests; Hepatology; Hospitalization; Hospitals; Hypoglycemia; Insulin; Laboratories; Medicine; Medicine & Public Health; Neuroendocrine tumors; Oncology; Original Article; Peptides; Software; Transplant Surgery; Tumors; 2-h OGTT; Hypoglycemia; Insulin; Insulinoma; C-peptide
• ISSN: 0163-2116; 1573-2568; 1573-2568
• DOI: 10.1007/s10620-020-06379-z

Background Insulinoma, owing to the low incidence and small volume of the tumor, is often undiagnosed. The 72-h fast test is centered on diagnosing insulinoma; however, it cannot be performed on outpatients. Our aim was to evaluate the results of a 3-h oral glucose tolerance test (3-h OGTT) for insulinoma diagnosis. Methods Thirty-seven patients with insulinoma were enrolled for comparison with 42 control subjects. All patients underwent 3-h OGTT with measurements of insulin and C-peptide. The secretion ratios of insulin and C-peptide at 1, 2, and 3 h were calculated by comparison with their values at 0 h. We used logistic regression analysis to establish the predictive models and compared the diagnostic efficiency by receiver operating characteristic analysis. Results The fasting insulin and C-peptide levels of insulinoma patients were both higher; however, the concentrations at 1 h and 2 h were both lower ( P  < 0.05). The levels at 3 h were not significantly different ( P  > 0.05). Our final logistic regression model was constructed as follows: logit ( P ) = 8.305 − 0.441 × insulin 2 h/0 h ratio − 1.679 × C-peptide 1 h/0 h ratio. A cutoff value of > 0.351 showed the highest diagnostic accuracy, with an area under the curve of 0.97, a sensitivity of 86.5%, and a specificity of 95.2%. Conclusions The 2-h/0-h insulin ratio, as well as the 1-h/0-h C-peptide ratio, has high diagnostic efficiency for insulinoma. The 2-h OGTT can be an alternative test for diagnosing insulinoma in outpatient settings.