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

Aims/hypothesis 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/interpretation 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.

Random non-fasting C-peptide testing can identify patients with insulin-treated type 2 diabetes at high risk of hypoglycaemia

“…Our findings of a strong association between C-peptide and hypoglycaemia are consistent with previous findings in type 1 diabetes using self-reported hypoglycaemia [1, 3, 9, 10, 19] and CGM studies in type 1 diabetes demonstrating higher SD or CV (SD/glucose), defined glucose variability and hypoglycaemia in individuals with lower C-peptide, including after islet transplant [27–29]. In these studies, C-peptide was measured using a mixed meal tolerance test, which is not suitable for routine use in clinical practice.…”

Beta cell function after intensive subcutaneous insulin therapy or intravenous insulin infusion at onset of type 1 diabetes in children without ketoacidosis

“…The significant association between HbA1c at diagnosis and beta‐cell function after 24 months emphasizes the significance of early diagnosis, and importance of the awareness of T1D in children and adolescents. The relationship between IDAA1c and C‐peptide peak after 24 months with 80% having C‐peptide >0.2 nmol/L when IDAA1c was <9% and 33% when it was >12, is similar to other published results …”

Stimulated urine C‐peptide creatinine ratio vs serum C‐peptide level for monitoring of β‐cell function in the first year after diagnosis of Type 1 diabetes

“…Both urine C‐peptide/creatinine ratio and AUC for serum C‐peptide correlated poorly with a clinical measure of β‐cell function, IDAA 1c , and with each other in the first 6 months, but improved over the second half of the follow‐up period. These findings are consistent with a report of serum analyses from the combined TrialNet studies, in which correlation between peak serum C‐peptide level and IDAA 1c strengthens as the 2‐year follow‐up of > 60 newly diagnosed participants progressed . Buckingham et al .…”

“…Buckingham et al . observed a correlation with IDAA 1c in the first 6 months after diagnosis in children, suggesting that the initial lack of correlation in the first 6 months in the present cohort may either be specific to adults or attributable to limited power in the present study combined with an attenuating effect of the intervention. However, Mortensen et al .…”