Background: No studies have examined endogenous insulin secretion in pediatric patients with type 1 diabetes in China using the gold-standard mixed-meal tolerance test. Because the latter is labor-intensive, we examined simpler surrogate markers of endogenous insulin secretion in Chinese youth, as previously reported for a European population.

Methods: Participants were 57 children and adolescents with type 1 diabetes aged 4.4-16.8 years (56% females). We performed 120-minute mixed-meal tolerance tests with serum C-peptide (CP) measurements every 30 minutes. Severe insulin deficiency (SID) was defined as CP peak < 0.2 nmol/L. Urine CP and creatinine levels were measured at 0 and 120 minutes.

Results: Twenty-five (44%) patients had SID. Fasting CP levels missed one case (96% sensitivity) with no false positives (100% specificity). While the 120-minute urine CP/creatinine had 100% sensitivity, it yielded markedly lower specificity (63%). Every 1-year increase in diabetes duration and 1-year decrease in age at diagnosis were associated with 37% (P < 0.001) and 20% (P = 0.005) reductions in serum CP area-under-the-curve, respectively. Thus, 86% of children aged < 5 years had SID compared to none among patients aged ≥ 11 years.