Highlight
- Serial glucose-adjusted dried blood spot (DBS) C-peptide sampling allows sensitive, home-based monitoring of β-cell function in recent-onset type 1 diabetes (T1D).
- Urine C-peptide-to-creatinine ratio (UCPCR) lacks sensitivity to detect early changes in β-cell function in the first 6 months post diagnosis.
- DBS sampling detected significant preservation of β-cell function in the Ustekinumab-treated intervention group earlier than traditional mixed-meal tolerance test (MMTT) measurements.
- Early DBS trends predicted 12-month MMTT C-peptide levels in controls, underscoring its potential as a prognostic tool in T1D trials.
Study Background
Type 1 diabetes (T1D) is characterized by autoimmune destruction of pancreatic β-cells, leading to insulin deficiency and lifelong dependence on exogenous insulin. Preservation of residual β-cell function after diagnosis is associated with better glycemic control and reduced complications. Accurately monitoring β-cell function is critical for evaluating the efficacy of therapeutic interventions aimed at halting or slowing disease progression.
The mixed-meal tolerance test (MMTT) remains the gold standard for assessing endogenous insulin secretion through stimulated C-peptide measurement. However, the MMTT is labor-intensive, costly, requires clinical visits, and is burdensome for patients, limiting its frequent use in clinical trials and routine care.
Less invasive alternatives, such as urine C-peptide-to-creatinine ratio (UCPCR) and dried blood spot (DBS) sampling of C-peptide, have been proposed to facilitate more frequent β-cell monitoring. Prior evidence on the sensitivity and temporal dynamics of these methods in reflecting early β-cell preservation has been limited.
The USTEKID trial assessed the immunomodulatory monoclonal antibody ustekinumab in adolescents with new-onset T1D. This substudy investigated the ability of serial UCPCR and DBS C-peptide sampling to detect β-cell function changes compared with MMTT over one year.
Study Design
This prospective interventional trial enrolled adolescents with recent-onset T1D. C-peptide was measured at three time points—screening, 28 weeks, and 52 weeks—using the 2-hour MMTT as the reference standard. UCPCR samples were collected following each MMTT visit. DBS samples were collected more frequently: fasting and 60 minutes postmeal samples were obtained weekly until week 28, then monthly until week 52.
Researchers compared UCPCR and glucose-adjusted DBS C-peptide results against contemporaneous MMTT data. Weekly DBS averages were calculated to assess temporal trends, using mixed linear models, bootstrap one-sample t tests, and autoregressive integrated moving average (ARIMA) models. Furthermore, the predictive value of six months of DBS data was evaluated for 12-month MMTT C-peptide outcomes.
Key Findings
The study reported distinctive temporal patterns in the markers evaluated:
- Urine C-Peptide-to-Creatinine Ratio (UCPCR): UCPCR levels remained stable during the first 6 months post diagnosis but demonstrated a decline by 12 months, mirroring the natural progression of β-cell loss. However, UCPCR was not sensitive enough to detect early changes or treatment effects within the initial 6-month period.
- Dried Blood Spot (DBS) C-Peptide: The area under the curve (AUC) for DBS C-peptide from 0 to 60 minutes postmeal declined steadily throughout 12 months, reflecting ongoing β-cell functional decline. Notably, DBS sampling detected a significantly slower decline in the intervention (ustekinumab-treated) group compared with controls as early as week 20 (P < 0.05). This early preservation was not apparent using UCPCR and only became detectable by MMTT at 52 weeks.
- Predictive Capability: The slope of DBS C-peptide decline over the first 6 months predicted 12-month MMTT C-peptide levels in the control group but not in the intervention group. This discrepancy aligns with the immunomodulatory effect of ustekinumab emerging after 6 months, highlighting DBS’s utility in detecting early treatment responses and the evolving disease trajectory.
These findings establish that frequent, glucose-adjusted DBS C-peptide sampling offers superior sensitivity compared to UCPCR and can provide earlier detection of β-cell preservation following therapeutic intervention.
Expert Commentary
The USTEKID substudy supports the growing consensus that frequent home-based DBS sampling is a practical and sensitive method for monitoring residual β-cell function in T1D clinical trials and potentially in clinical practice. By reducing the logistical constraints and patient burden associated with MMTT, DBS enables higher resolution tracking of β-cell dynamics in response to therapy. The study’s demonstration that DBS detected intervention effects four months earlier than MMTT emphasizes its clinical trial value for timely evaluation.
The limited sensitivity of UCPCR in early disease stages might be due to its higher variability and less direct correlation with stimulated insulin secretion compared to blood-based measures. While UCPCR remains a convenient, noninvasive tool, it should be considered less reliable for early-phase intervention studies.
One limitation is that DBS C-peptide measurement requires rigorous standardization and glucose adjustment to accurately reflect underlying β-cell function. Patient adherence to frequent sampling schedules and proper sample handling are logistical challenges to address in future implementations.
Overall, these findings resonate with current guideline calls for improved minimally invasive biomarkers to advance personalized approaches in T1D management and research.
Conclusion
Serial dried blood spot C-peptide sampling represents a significant advance for noninvasive, home-based monitoring of β-cell function in new-onset type 1 diabetes. This method surpasses urine C-peptide-to-creatinine ratio in sensitivity to early β-cell functional changes and detects therapeutic preservation of β-cell activity earlier than the traditional mixed-meal tolerance test. Adoption of frequent DBS sampling in clinical trials may accelerate evaluation of disease-modifying therapies, while its integration into clinical practice could support tailored treatment strategies to preserve endogenous insulin secretion and improve outcomes in patients with T1D.
Funding and ClinicalTrials.gov
The USTEKID trial was supported by grants from appropriate funding bodies (details as per original publication). The trial is registered at ClinicalTrials.gov with the identifier: NCT number (to be referenced from the original). Detailed information on funding and trial registration can be accessed through the original Diabetes Care article by Dunseath et al.
References
1. Dunseath GJ, Cheung WY, Luzio SD, et al. Serial Dried Blood Spot C-Peptide Sampling, but Not Urine C-Peptide-to-Creatinine Ratio, Detects Early Preservation of β-Cell Function in New-Onset Type 1 Diabetes: Experience From the USTEKID Trial. Diabetes Care. 2026 Jul;49(7):1213-1220.
2. Oram RA, Jones AG, Besser REJ, Walker JN, Shields BM, Brown RJ, Knight BA, McDonald TJ, Hattersley AT. The C-peptide and Urine C-peptide-to-creatinine ratio (UCPCR): emerging clinical biomarkers in diabetes. Diabet Med. 2014;31(2):141-9.
3. Greenbaum CJ, Beam CA, Boulware D, et al. Preservation of C-peptide in Type 1 Diabetes: Four Years of Follow-Up in the TrialNet Natural History Study. Diabetes. 2012;61(11):2376-2382.
4. American Diabetes Association. 2. Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S17-S38.