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. 2016 Jun;39(6):e76-8.
doi: 10.2337/dc15-2077. Epub 2016 Apr 13.

Two- and Four-Hour Tests Differ in Capture of C-Peptide Responses to a Mixed Meal in Type 1 Diabetes

Karen D Boyle  1 , Lynette Keyes-Elstein  2 , Mario R Ehlers  3 , James McNamara  4 , Mark R Rigby  5 , Stephen E Gitelman  6 , Lia J Weiner  2 , Kristen L Much  2 , Kevan C Herold  7
Affiliations

Two- and Four-Hour Tests Differ in Capture of C-Peptide Responses to a Mixed Meal in Type 1 Diabetes

Karen D Boyle et al. Diabetes Care. 2016 Jun.
No abstract available

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Figures

Figure 1
Figure 1
Analysis of 2- and 4-h C-peptide AUCs during MMTTs. The C-peptide AUC was computed for 2 and 4 h at baseline and at months 12 and 24 using the trapezoidal rule; mAUCs were computed by dividing AUCs by the duration of the test, 120 or 240 min, as indicated. Sdiff equals the 2-h mAUC minus the 4-h mAUC in SD units. Within each trial, the values below the lower limit of detection were either assigned a value of one-half of the lower limit of detection (START and T1DAL) or 0 (AbATE). Only available data were used in these analyses; missing MMTTs were not imputed. A: 2- to 4-h C-peptide mAUC estimates. Data from all control subjects over 24 months are shown and from drug-treated subjects at month 12. Root mean square error (RMSE) was derived from ANCOVA models controlling for baseline mAUC. Six subjects without baseline data were excluded. For active treatment groups at baseline and month 24, SDs for 2-h tests were greater than for 4-h tests (data not shown) except for T1DAL at month 24 where SDs were 0.51 and 0.52 for 2-h and 4-h tests, respectively. B: Sdiff by peak C-peptide value. The peak C-peptide value is the observed measurement with the highest value. The solid line shows the average trend. C: Sdiff by time at peak C-peptide point. The top and bottom of each box represent the 75th and 25th percentiles, respectively. The line through each box is the median. The whiskers mark the last points within 1.5 times the interquartile range. The solid line connects the averages for each visit across C-peptide time points. D: Sdiffs over time for individuals by study. Lines connect Sdiffs over time for individual subjects. Line styles reflect baseline Sdiffs in tertiles. Six subjects without baseline data were excluded. Solid light gray lines represent the lower tertile (values <–0.34). Hashed dark gray lines represent the upper tertile (values >0.22). Black dotted lines represent the middle tertile. E: Sdiffs for untreated pediatric and adult subjects by visit. Box plots for pediatric and adult subjects are black and gray, respectively. See C for a description of box plots. Black triangles represent mean values. F: Sdiff at month 12 in the AbATE study. The distribution of Sdiffs was shifted to the right for treated subjects (top) indicating that the 2-h mAUC overestimated the 4-h mAUC. The distribution of Sdiffs was shifted to the left for placebo subjects (bottom) indicating that the 2-h mAUC underestimated the 4-h mAUC. Thus these changes suggest that the C-peptide responses changed differently in the drug and placebo subjects over time and that the precision of the 2-h test differed for the two groups. The opposite effect was seen in the START study (data not shown).
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References

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