Sims, Emily K.Bahnson, Henry T.Nyalwidhe, JuliusHaataja, LeenaDavis, Asa K.Speake, CateDiMeglio, Linda A.Blum, JaniceMorris, Margaret A.Mirmira, Raghavendra G.Nadler, JerryMastracci, Teresa L.Marcovina, SanticaQian, Wei-JunYi, LianSwensen, Adam C.Yip-Schneider, MicheleSchmidt, C. MaxConsidine, Robert V.Arvan, PeterGreenbaum, Carla J.Evans-Molina, CarmellaT1D Exchange Residual C-peptide Study Group2020-04-132020-04-132019-02Sims, E. K., Bahnson, H. T., Nyalwidhe, J., Haataja, L., Davis, A. K., Speake, C., DiMeglio, L. A., Blum, J., Morris, M. A., Mirmira, R. G., Nadler, J., Mastracci, T. L., Marcovina, S., Qian, W. J., Yi, L., Swensen, A. C., Yip-Schneider, M., Schmidt, C. M., Considine, R. V., Arvan, P., … T1D Exchange Residual C-peptide Study Group (2019). Proinsulin Secretion Is a Persistent Feature of Type 1 Diabetes. Diabetes care, 42(2), 258–264. https://doi.org/10.2337/dc17-2625https://hdl.handle.net/1805/22558OBJECTIVE: Abnormally elevated proinsulin secretion has been reported in type 2 and early type 1 diabetes when significant C-peptide is present. We questioned whether individuals with long-standing type 1 diabetes and low or absent C-peptide secretory capacity retained the ability to make proinsulin. RESEARCH DESIGN AND METHODS: C-peptide and proinsulin were measured in fasting and stimulated sera from 319 subjects with long-standing type 1 diabetes (≥3 years) and 12 control subjects without diabetes. We considered three categories of stimulated C-peptide: 1) C-peptide positive, with high stimulated values ≥0.2 nmol/L; 2) C-peptide positive, with low stimulated values ≥0.017 but <0.2 nmol/L; and 3) C-peptide <0.017 nmol/L. Longitudinal samples were analyzed from C-peptide-positive subjects with diabetes after 1, 2, and 4 years. RESULTS: Of individuals with long-standing type 1 diabetes, 95.9% had detectable serum proinsulin (>3.1 pmol/L), while 89.9% of participants with stimulated C-peptide values below the limit of detection (<0.017 nmol/L; n = 99) had measurable proinsulin. Proinsulin levels remained stable over 4 years of follow-up, while C-peptide decreased slowly during longitudinal analysis. Correlations between proinsulin with C-peptide and mixed-meal stimulation of proinsulin were found only in subjects with high stimulated C-peptide values (≥0.2 nmol/L). Specifically, increases in proinsulin with mixed-meal stimulation were present only in the group with high stimulated C-peptide values, with no increases observed among subjects with low or undetectable (<0.017 nmol/L) residual C-peptide. CONCLUSIONS: In individuals with long-duration type 1 diabetes, the ability to secrete proinsulin persists, even in those with undetectable serum C-peptide.en-USPublisher PolicyC-PeptideCohort StudiesDiabetes Mellitus, Type 1FastingInsulinMealsProinsulinTime FactorsArticle