We investigated residual beta cell function in participants from the DCCT/EDIC study with an average of 35 (range 27, 48) years duration of T1D. Between 2015-2017 after 22-24 years of follow-up in EDIC, a 4-hour mixed meal tolerance test was administered to 944 participants and 7 timed plasma specimens were collected and assayed for C-peptide using a chemiluminescent immunoassay (Roche). We defined a significant post-stimulus response as a peak C-peptide concentration >0.03 nmol/L, based on an earlier DCCT study which demonstrated that the risk of microvascular disease progression was markedly higher among participants who entered the trial with values below this concentration. Overall, 71 (7.5%) participants were classified as “responders” with a median peak C-peptide of 0.10 nmol/L (IQR 0.06, 0.15). Among the 873 participants classified as “non-responders”, 46 had detectable peak C-peptide between 0.003 (limit of detection) and 0.029 nmol/L. Responders were slightly older than non-responders (58.5 ± 6.2 vs. 56.5 ± 6.8 y; p=0.02), yet had similar age of onset of diabetes (22.5 ± 7.0 vs. 21.4 ± 7.8 y) and duration of diabetes (35.9 ± 5.1 vs. 35.0 ± 4.9 y). Compared to non-responders, responders had lower HbA1c values (8.6 ± 1.7 vs. 8.9 ± 1.5%; p=0.01) and higher stimulated C-peptide (0.22 ± 0.14 vs. 0.11 ± 0.11 nmol/L; p<0.0001) at DCCT baseline; and had lower insulin requirements both at DCCT baseline (0.54 ± 0.18 vs. 0.67 ± 0.24 units/kg/day; p<0.0001) and throughout DCCT follow-up (0.61 ± 0.20 vs. 0.69 ± 0.19 units/kg/day; p=0.0008). Significantly fewer responders experienced severe hypoglycemia [requiring assistance] throughout the DCCT/EDIC study (45% of responders vs. 70% of non-responders; p<0.0001). Both the initial episode and recurrent episodes of severe hypoglycemia were less frequent with increasing C-peptide concentrations.
In conclusion, beta cell function persists in some very long duration T1D patients and is associated with clinically meaningful reductions in the frequency of severe hypoglycemia.
R. Gubitosi-Klug: None. B. Braffett: None. S.M. Hitt: None. V. Arends: None. M. Steffes: None. A.K. Saenger: Advisory Panel; Self; Alere Inc. J. Lachin: Board Member; Self; AbbVie Inc., Celgene Corporation. J.P. Palmer: None.