Background Type 1 diabetes is characterized by pancreatic beta-cell destruction and an inability to synthesize insulin. Connecting peptide (C-peptide) is formed from the same precursor as insulin and is produced in equimolar amounts as insulin. There are several clinical trials currently being performed to explore the possibility of beta-cell preservation or regeneration. Most children are not eligible for these trials because it is often presumed that C-peptide levels will decrease and become undetectable after years of having type 1 diabetes. Several studies in the adult population have demonstrated that C-peptide may remain measureable in patients who have had diabetes for up to 50 years after diagnosis. Recently, it was demonstrated that 10% of adult patients who have had type 1 diabetes for 31-40 years have measureable levels of serum C-peptide if measured with an ultrasensitive assay. The levels were lower in patients who had diabetes for a longer time. This pattern was also demonstrated in the Diabetes Control and Complications Trial (DCCT) and NHANES trial. No studies have been performed exclusively in pediatric patients Hypothesis The investigators hypothesize that C-peptide should be detectable in the sera of pediatric patients who have had type 1 diabetes for greater than 1 year and as far out as > 20 years after diagnosis. The investigators also hypothesize that since their patient population has had diabetes for less time as compared to adults, the levels of C-peptide should be higher than reported for adults and that a greater proportion of patients in the pediatric population will have detectable C-peptide levels as compared to adults.

1) Objectives:

1. To determine if C-peptide is detectable in the sera of children that have had type 1 diabetes for more than 1 year using an ultrasensitive assay.
2. To correlate C-peptide levels with duration since diagnosis, current age, antibody titers at diagnosis, hemoglobin A1c, total daily insulin dosage.
3. To determine responsiveness of residual C-peptide to mixed-meal testing.

Inclusion Criteria:

• Male or female
• 1-25 years of age
• Have had type 1 diabetes for more than 1 year.

Exclusion Criteria:

• Does not meet inclusion criteria
• Foster children
• Patients without primary caregiver
• Pregnant

Subjects will be recruited from the population of patients seen in the Division of Pediatric Endocrinology and Diabetes. These patients must have type 1 diabetes and must have been diagnosed more than 1 year prior to their recruitment. Potential subjects will be identified by reaching out to the physicians in the division and asking that they inform the investigators of patients that they see with type 1 diabetes. Those patients will have their information reviewed by the investigators using EPIC, the electronic medical record at The Mount Sinai Hospital.