Early Detection of Beta-Cell Decline using Home Dried Blood Spot C-Peptide Levels in New-Onset Type 1 Diabetes

Objective: There is a need for early detection of beta-cell decline in people with newly diagnosed (ND) type 1 diabetes. The gold standard mixed-meal tolerance test (MMTT) is an invasive and time-consuming procedure, that requires participants to travel to clinical sites. We assessed the feasibility of measuring dried blood spot (DBS) C-peptide levels collected at home as an alternative to the MMTT to detect early beta-cell decline.

Research Design and Methods: Individuals with ND type 1 diabetes recruited within six weeks of diagnosis as part of the INNODIA cohort, collected finger-prick DBS C-peptide at home, both fasting and 60 minutes post liquid meal. At 12 months, an MMTT was conducted to measure venous C-peptide area under the curve (AUC).

Results: A total of 292 people were analysed, mean age was 12.7 years (range 1.2–43.8 years). The median [IQR] number of DBS card pairs per participant was 6.5 [2–9] over 12 months. The slopes of stimulated DBS C-peptide in the first six months significantly predicted venous MMTT AUC C-peptide and peak C-peptide at 12 months (p<0.01). The models were adjusted for simultaneous glucose levels, age, and baseline fasting C-peptide. However, the six-month fasting DBS C-peptide slope did not predict 12-month MMTT AUC C-peptide.

Conclusions: Home DBS C-peptide assessment is a feasible method to monitor beta-cell function in ND type 1 diabetes. The early prognostic utility of stimulated DBS C-peptide highlights its potential for optimising trial design. However, further validation is needed to confirm its reliability and broader applicability.