Diabetes Care, Vol 16, Issue 6 911-915, Copyright © 1993 by American Diabetes Association
Comparison of bolus and infusion protocols for determining acute insulin response to intravenous glucose in normal humans. The ICARUS Group. Islet Cell Antibody Register User's Study
DK McCulloch, PJ Bingley, PG Colman, RA Jackson and EA Gale
Diabetes Clinical Research Unit, Virginia Mason Research Center, Seattle, WA 98101.
OBJECTIVE--To help standardize methodology for intravenous glucose
tolerance testing in preclinical IDDM by comparing a 30-s bolus and a 3-min
infusion of glucose. RESEARCH DESIGN AND METHODS--We tested 20 healthy
nondiabetic adults at four centers (in Seattle, Boston, Melbourne, and
London). Each subject had four intravenous glucose tolerance tests (two
bolus and two infusion). The acute insulin response to glucose was
calculated as the mean of the 1' + 3', the mean of 1' to 10', or as the
integrated area from 0 to 10'. Glucose and insulin profiles and
intrasubject coefficient of variation were compared. RESULTS--With the
infusion protocol, the 1' insulin was significantly higher, resulting in a
higher acute insulin response to glucose when calculated as 1' + 3' (525
+/- 66 vs. 376 +/- 35 pM, P < 0.004). When calculated over 10 min,
however, the acute insulin response to glucose was not different between
protocols. In addition, the intrasubject coefficient of variation was
significantly better when calculated over 10 min in both protocols, but no
significant differences were noted between the bolus and infusion
(infusion: AIRg [area from 0 to 10'] 10.4 +/- 2.1% vs. AIRg [1' + 3'] 14.9
+/- 2.8%, P < 0.007; bolus: AIRg [area from 0 to 10'] 14.6 +/- 2.8% vs.
AIRg [1' + 3'] 19.8 +/- 3.5%, P < 0.007). Comparison of the insulin
assays between the four centers showed close correlation and gave
indistinguishable results in terms of within-subject coefficient of
variation. Glucose profiles were similar in both protocols. Although the
glucose values were lower with the bolus protocol from 4' to 40', the rate
of fall from 10 to 30' (and thus the rate of glucose disposal) was
indistinguishable between the two. CONCLUSIONS--These data suggest that
neither protocol gives significant advantage over the other. However, to
allow comparison of the acute insulin response to glucose between different
protocols used in centers around the world, the ICARUS 3-min infusion
protocol is recommended, with acute insulin response to glucose calculated
over 10 min after the end of glucose administration; this reduces the
within-subject coefficient of variation and provides similar acute insulin
response to glucose with both protocols.