How Reliable Is the Euglycaemic Hyperinsulinemic Clamp Test for the Confirmation of Autonomous Endogenous Hyperinsulinemia ?

Summary

Inhibition of C-Peptide secretion by exogenous insulin was studied during euglycemic clamp in 13 patients with histologicaly verified causes of organic hyperinsulinaemia (10 with beta cell adenoma ; 2 with beta cell carcinoma and 1 with beta cell hyperplasia) and in 10 healthy controls. Euglycemic clamps were performed using artificial endocrine pancreas (Clamp Mode 9 :1) while insulin infusion (Humulin Normal—Lilly) rate was 0.1 U/kg BW/h. Blood samples for serum insulin (RIA INEP) and C-Feptide (RIA-Biodata) were taken at 0 ; 30 ; 60 ; 90 and 120 min. Statistical analysis was done using SPSS on IBM-PC with Wilcoxon sum rank test and one way ANOVA. All the patients were studied before the operation and in four of them clamp studies were repeated after the operation. Statistically significant suppression of C-Peptide values in 120 min was established in the control group (p less than 0.05) while there was no significant suppression in insulinoma group (p greater than 0.05), except in one patient with beta cell hyperplasia. Various types of responses (suppression, no change, paradoxical increase) were observed after the operation in the insulinoma group. Possible mechanisms and the meanings of the absence of insulin induced C-Peptide suppression in insulinoma group are discussed. It is concluded that euglycemic hyperinsulinemic clamp study could be useful and a complementary test to other established tests for the confirmation of the diagnosis of insulinoma. Further work on beta cell response after the operation in patients with insulinoma is necessary.

Key words

Insulinoma - Euglycemic clamp - C-Peptide suppression