The continuous low dose insulin and glucose infusion test: a simplified and accurate method for the evaluation of insulin sensitivity and insulin secretion in population studies
PM Piatti, LD Monti, A Caumo, G Santambrogio, F Magni, M Galli-Kienle, S Costa, AE Pontiroli, KG Alberti and G Pozza
Istituto Scientifico San Raffaele, Cattedra di Clinica Medica, Universita di Milano, Italy.
In this study we investigated a simple nonlabor-intensive method to
evaluate insulin sensitivity and beta-cell function which is suitable for
application in population studies. The method is a refinement of the
modified Harano test and consists of a continuous low dose insulin (25
mU/kg.h) and glucose (4 mg/kg.min) infusion test (LDIGIT) lasting 150 min.
Insulin sensitivity was evaluated as the MCR of glucose divided by the
steady state serum insulin level achieved at the end of the test. Insulin
secretion was expressed as the incremental area for C- peptide
concentration during the first 15 min of the test. We compared the indices
of insulin sensitivity and insulin secretion yielded by LDIGIT with those
derived from the euglycemic clamp and the hyperglycemic clamp,
respectively. Fifty-four subjects underwent a LDIGIT (33 with normal
glucose tolerance and 21 with impaired glucose tolerance); of the 54, 19
were submitted to a euglycemic clamp, 18 to a hyperglycemic clamp, and 10
to a modified Harano test (insulin infusion, 50 mU/kg.h; glucose infusion,
6 mg/kg.min). LDIGIT overcame the drawbacks associated with the modified
Harano test because it resulted in more stable final glucose levels and
prevented the occurrence of hypoglycemic episodes. No significant
differences were found between the insulin sensitivity index (ISI) of the
LDIGIT and that of the euglycemic clamp for each group of subjects.
Moreover, there was a strong correlation between the ISI determined by
LDIGIT and the ISI determined by clamp (r = 0.90; P < 0.0001), and the
best regression line was not different from the identity line, suggesting
that the two indices are equivalent. The index of insulin secretion
provided by LDIGIT correlated well with that of the hyperglycemic clamp (r
= 0.82; P < 0.001) and was significantly higher in overweight subjects
than in normal weight subjects. In conclusion, LDIGIT is a simple and
accurate method to assess insulin sensitivity and secretion. It can be
useful in population studies and in situations when more complex techniques
are not feasible.
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