PMID- 31895699 OWN - NLM STAT- MEDLINE DCOM- 20201230 LR - 20221229 IS - 1558-8238 (Electronic) IS - 0021-9738 (Print) IS - 0021-9738 (Linking) VI - 130 IP - 4 DP - 2020 Apr 1 TI - High residual C-peptide likely contributes to glycemic control in type 1 diabetes. PG - 1850-1862 LID - 134057 [pii] LID - 10.1172/JCI134057 [doi] AB - BACKGROUNDResidual C-peptide is detected in many people for years following the diagnosis of type 1 diabetes; however, the physiologic significance of low levels of detectable C-peptide is not known.METHODSWe studied 63 adults with type 1 diabetes classified by peak mixed-meal tolerance test (MMTT) C-peptide as negative (<0.007 pmol/mL; n = 15), low (0.017-0.200; n = 16), intermediate (>0.200-0.400; n = 15), or high (>0.400; n = 17). We compared the groups' glycemia from continuous glucose monitoring (CGM), beta cell secretory responses from a glucose-potentiated arginine (GPA) test, insulin sensitivity from a hyperinsulinemic-euglycemic (EU) clamp, and glucose counterregulatory responses from a subsequent hypoglycemic (HYPO) clamp.RESULTSLow and intermediate MMTT C-peptide groups did not exhibit beta cell secretory responses to hyperglycemia, whereas the high C-peptide group showed increases in both C-peptide and proinsulin (P