[Study of the beta cell function in type I diabetes by the determination of peptide C after glucagon challenge]

In 35 patients (13F/22M; age range 2-15 years), affected by insulin dependent diabetes mellitus (IDDM), basal and glucagon stimulated C peptide was determined and correlated with the daily insulin requirement (U/Kg/die), the glycosylated hemoglobin (HbA1c), the age of onset (months) and the length of the illness (months). The results of C peptide determinations are illustrated in tab. 1: in 20 patients (group I) the basal value of C peptide is higher than 1 ng/ml and increases after glucagon load; in 15 patients (group II) the basal value of C peptide is lower than 1 ng/ml; in 9 ones (group IIA) of these 15 a glucagon load does not elicit a residual insulin secretion; in the other 6 ones (group IIB) a significative C peptide increase is observed after glucagon load. A better metabolic control (p less than 0.01); Student t test) and a shorter length of the illness (p less than 0.05; Mann-Withney U test) was noticed in the group I in comparison with the group IIA, in which no insulin reserve, even after glucagon load, was demonstrated (tab. 2). However, no difference in the metabolic control, insulin requirement, age of onset or length of the illness resulted between group IIA and group IIB (in which an insulin reserve had been demonstrated only after glucagon load). The basal C peptide evaluation and follow up is useful in the assessment of the individual case of IDDM: a glucagon load may demonstrate a residual insulin reserve in some patients with a low basal C peptide.