Diagnostic utility of the insulin-to-C-peptide molar ratio in differentiating insulin autoimmune syndrome and exogenous insulin antibody syndrome from insulinoma

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The study evaluated the insulin-to-C-peptide molar ratio for distinguishing insulin autoimmune syndrome (IAS) and exogenous insulin antibody syndrome (EIAS) from insulinoma.
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The insulin-to-C-peptide molar ratio was significantly higher in IAS and EIAS compared to insulinoma during fasting and hypoglycemic episodes.
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Optimal cutoffs for the insulin-to-C-peptide molar ratio were identified as 0.382 for IAS and 0.552 for EIAS during hypoglycemic episodes.
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In the fasting state, optimal cutoffs for IAS and EIAS were determined to be 0.309 and 0.386, respectively, improving sensitivity compared to the conventional cutoff of 1.
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The study suggests that lower cutoffs for the insulin-to-C-peptide molar ratio may enhance diagnostic sensitivity while maintaining specificity for IAS and EIAS.

Frontiers In Endocrinology

by Yang Wang, Yiwen Liu, Jie Yu, Baodi Xing, Fan Ping, Wei Li, Lingling Xu, Ming Li, Huabing Zhang, Yuxiu Li
July 7, 2026

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