C-peptide in dried blood spots.

Area of Science:

• Endocrinology
• Biochemistry
• Clinical Diagnostics

Background:

• C-peptide is a key biomarker for assessing endogenous insulin production and beta cell function.
• Traditional serum C-peptide analysis requires venous blood draws, which can be invasive and challenging for frequent monitoring.
• Dried Blood Spot (DBS) sampling offers a less invasive alternative for biological sample collection.

Purpose of the Study:

• To evaluate the feasibility and accuracy of the Dried Blood Spot (DBS) technique for analyzing C-peptide levels.
• To develop and validate a conversion formula for estimating serum C-peptide from DBS samples.
• To assess the stability of C-peptide in DBS samples over time.

Main Methods:

• Serum C-peptide (S-C-peptide) and paired whole blood samples on filters were collected from 198 healthy subjects.
• A conversion formula was derived using a subset of subjects, incorporating DBS-C-peptide, storage time, and age.
• The formula was cross-validated on the entire population using Bland-Altman analysis.

Main Results:

• A robust conversion formula was established: (log S-C-peptide = 1.696 + 1.367 log DBS-C-peptide + 0.058 (storage time/month) + 0.014 (age/10 years)).
• Bland-Altman plots showed excellent agreement between converted DBS-C-peptide and S-C-peptide at baseline (mean difference 0, limits of agreement -0.18 to +0.18).
• C-peptide levels in DBS samples remained stable for up to six months, with minimal deviation from baseline values.

Conclusions:

• The DBS-C-peptide technique is a viable and accurate method for analyzing C-peptide.
• DBS-C-peptide can serve as a reliable first-line screening test for monitoring normal beta cell function.
• The stability of C-peptide in DBS samples supports its use for longitudinal monitoring and remote sample collection.