A 60 minute hyperglycemic clamp is sufficient to assess both phases of insulin secretion

The hyperglycemic clamp is considered to be the gold standard for determini ng both first and second phase insulin secretion. In order to achieve a rea sonable insulin plateau for the second phase, it has become common practice to clamp for 120 or even 180 minutes at 10 mM. It is unknown whether earli er insulin determinations would be sufficient to predict second phase insul in secretion. We therefore reviewed the hyperglycemic clamp data of 58 subj ects with different deg rees of glucose tolerance to assess whether one or more insulin concentrations determined at earlier time points of the clamp could predict second phase insulin secretion (insulin and C-peptide concent ration at 120 minutes). The correlation coefficients between second-phase i nsulin secretion and plasma insulin or C-peptide at 60 min were 0.95 and 0. 96, respectively (both p<0.00005). Averaging plasma insulin or C-peptide ov er 2 or more adjacent time points did not improve the correlation. In concl usion, a one-hour hyperglycemic clamp can provide the standard measurement of first phase insulin secretion plus a good approximation of second phase insulin secretion.