Distinguishing Insulinoma From Reactive Hypoglycemia: Characteristic Glycemia Patterns During the 5-Hour Oral Glucose Tolerance Test

<h2>Abstract</h2><h3>Context</h3> Individuals with insulinoma may develop post glucose load hypoglycemia. <h3>Objective</h3> To characterize the glucose, insulin, and C-peptide values of patients with insulinoma and reactive hypoglycemia (RH) during a 5-hour oral glucose tolerance test (5h-OGTT). <h3>Methods</h3> A retrospective study was conducted involving 85 inpatients (57 with insulinoma, 28 with RH). 5h-OGTT with frequent blood sampling of glucose, insulin, and C-peptide were performed in 22 patients with insulinoma and 28 patients with RH. <h3>Results</h3> The insulinoma group had a higher body mass index (25.51 ± 4.03 vs 22.84 ± 4.92 kg/m², <i>P</i> = 0.01) but lower HbA1c (4.68 ± 0.52% vs 5.28 ± 0.51%, <i>P</i> < 0.01) compared to the RH group. Fasting glucose was significantly lower in the insulinoma group (53.34 ± 23.31 vs 81.77 ± 12.48 mg/dL, <i>P</i> < 0.01), concomitant with higher fasting insulin (16.99 ± 17.71 vs 7.65 ± 5.51 uU/mL, <i>P</i> < 0.01), and C-peptide (1.25 ± 0.67 vs 0.68 ± 0.32 nmol/L, <i>P</i> < 0.01). Fasting insulin: fasting glucose ratio were higher for insulinoma vs RH (0.38 ± 0.49 vs 0.09 ± 0.07 uU/ml: mg/dL, <i>P</i> = 0.0035). During the 5h-OGTT, blood glucose levels were significantly lower at 0 hour (55.39 ± 16.03 vs 80.04 ± 7.24 mg/dL), and 5-hour (49.35 ± 8.77 vs 70.4 ± 12.76 mg/dL) in the insulinoma group (<i>P</i> < 0.0001 for both). No differences were found in the area under the curve of insulin and C-peptide. <h3>Conclusion</h3> Distinct glycemia patterns, particularly lower fasting and 5-hour glucose levels during OGTT, effectively differentiate insulinoma from RH.