Microsampling Collection Methods for Measurement of C-peptide in Whole Blood

Abstract

Background: Microsampling techniques are alternative methods to venous sampling for obtaining blood for measurement of circulating biomarkers, offering the convenience of reduced sample volume and elimination of the need for phlebotomists. Dried blood spot (DBS) microsampling methods have been used for many years while more recently a volumetric absorptive microsampling device (VAMS™) has been introduced. In diabetes mellitus, circulating C-peptide is commonly used as an indicator of endogenous insulin secretion and clinical measurement can aid in diagnosis as well as informing on therapy. This pilot study investigated the effectiveness of microsampling collection of capillary blood for measurement of C-peptide.

Methods: Capillary blood was collected into capillary tubes and centrifuged for plasma samples. Simultaneous samples were also collected using both microsampling methods (DBS and VAMS). Blood from both microsamplers was extracted prior to assaying for C-peptide alongside the corresponding plasma samples, using specific immunoassays and results obtained from microsampling compared to the reference plasma concentrations. Stability was determined by collecting duplicate DBS and VAMS and assaying both in a single assay after storing one at -20°C immediately and one at room temperature for 48 hours post-collection.

Results: Good agreement was observed between C-peptide concentrations in plasma and equivalent DBS and VAMS samples ( R² = .929 and .9231, DBS and VAMS, respectively), with mean differences of 75.7 and 8.4 pmol/L observed for DBS and VAMS. Small decreases in C-peptide of 11.6% and 0.1% were observed after 48 hours storage for DBS and VAMS, respectively.

Conclusions: C-peptide collected using DBS and VAMS showed good agreement with reference plasma concentrations, suggesting both would be an effective microsampling method for collection and measurement of C-peptide.

Keywords: C-peptide; dried blood spot; microsampling; volumetric absorptive microsampling.

Figure 1.

Relationship between plasma C-peptide and DBS (closed circles, solid regression line) or VAMS (open circles, dashed regression line) plasma equivalent C-peptide concentrations measured in the chemiluminescence assay.

Figure 2.

Difference plots for plasma C-peptide versus plasma equivalent (a) DBS and (b) VAMS C-peptide concentrations assayed using chemiluminescence assay.