title: CGM-measured glucose values have a strong correlation with C-peptide, HbA1c and IDAAC, but do poorly in predicting C-peptide levels in the two years following onset of diabetes.
abstract: OBJECTIVE
  The aim of this work was to assess the association between continuous glucose monitoring (CGM) data, HbA1c, insulin-dose-adjusted HbA1c (IDAA1c) and C-peptide responses during the first 2 years following diagnosis of type 1 diabetes.
  
  
  METHODS
  A secondary analysis was conducted of data collected from a randomised trial assessing the effect of intensive management initiated within 1 week of diagnosis of type 1 diabetes, in which mixed-meal tolerance tests were performed at baseline and at eight additional time points through 24 months. CGM data were collected at each visit.
  
  
  RESULTS
  Among 67 study participants (mean age [± SD] 13.3 ± 5.7 years), HbA1c was inversely correlated with C-peptide at each time point (p < 0.001), as were changes in each measure between time points (p < 0.001). However, C-peptide at one visit did not predict the change in HbA1c at the next visit and vice versa. Higher C-peptide levels correlated with increased proportion of CGM glucose values between 3.9 and 7.8 mmol/l and lower CV (p = 0.001 and p = 0.02, respectively) but not with CGM glucose levels <3.9 mmol/l. Virtually all participants with IDAA1c < 9 retained substantial insulin secretion but when evaluated together with CGM, time in the range of 3.9-7.8 mmol/l and CV did not provide additional value in predicting C-peptide levels.
  
  
  CONCLUSIONS
  In the first 2 years after diagnosis of type 1 diabetes, higher C-peptide levels are associated with increased sensor glucose levels in the target range and with lower glucose variability but not hypoglycaemia. CGM metrics do not provide added value over the IDAA1c in predicting C-peptide levels.
authors.affiliation: Department of Pediatrics, Stanford University School of Medicine, Palo Alto, CA, USA.
authors.forename: Bruce
authors.initials: B
authors.lastname: Buckingham
authors.forename: Peiyao
authors.initials: P
authors.lastname: Cheng
authors.forename: Roy W
authors.initials: RW
authors.lastname: Beck
authors.forename: Craig
authors.initials: C
authors.lastname: Kollman
authors.forename: Katrina J
authors.initials: KJ
authors.lastname: Ruedy
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Weinzimer
authors.forename: Robert
authors.initials: R
authors.lastname: Slover
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Bremer
authors.forename: John
authors.initials: J
authors.lastname: Fuqua
authors.forename: William
authors.initials: W
authors.lastname: Tamborlane
mesh_terms: D000293:Adolescent; D000328:Adult; D001786:Blood Glucose / Q000032:analysis*; D015190:Blood Glucose Self-Monitoring; D002096:C-Peptide / Q000097:blood*; D002648:Child; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D005951:Glucose Tolerance Test; D006442:Glycated Hemoglobin / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000008:administration & dosage*; D007332:Insulin Infusion Systems; D008875:Middle Aged; D012016:Reference Values; D055815:Young Adult
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D006442:Glycated Hemoglobin; D007328:Insulin; C517652:hemoglobin A1c protein, human