28-hour profiles of blood glucose (BG), plasma immunoreactive insulin (IRI) and IRI/BG ratio in four insulinomas.

Nycthemeral variations in blood glucose (BG) and insulinemia (IRI) of four subjects with insulin-secreting pancreatic tumors were determined. Blood samples were drawn every 15 min over a 28-h period. After surgery, two of the subjects were retested. Meals were distributed during testing so that there was a minimum of eight meals per test. The meals before and after surgery were qualitatively, quantitatively and chronologically the same. Even though the circadian profiles of the glycemia and insulinemia varied greatly among the subjects, there were three common characteristics during the noctural period (24 h-8 h): Existence of one or several phases of at least 1 hour where the glycemia was less than 2.78 mmol/l, Existence of IRI peaks, without eating. Existence of a peak or of increased values (as compared to normal values) of the IRI/BG ratio, without eating. The IRI/BG ratio is a very sensitive index for insulin secretion dysfunction as compared to glycemia. The results suggest that the measurement of glycemia and insulinemia of sleeping subjects and then calculation of the IRI/BG ratio is sufficient to affirm the presence of an insulin-secreting adenoma.