Six methods for the determination of C-peptide evaluated

Area of Science:

• Clinical Chemistry
• Assay Development

Background:

• C-peptide is a vital biomarker for assessing endogenous insulin production.
• Accurate C-peptide measurement is crucial for diagnosing and managing diabetes.
• Variability in assay performance can impact clinical interpretation.

Purpose of the Study:

• To evaluate and compare the performance of six different C-peptide assays.
• To identify potential biases and limitations in current C-peptide measurement methods.
• To provide recommendations for improving C-peptide assay standardization and laboratory practice.

Main Methods:

• Evaluation of six C-peptide assays: five radioimmunoassays and one chemiluminescence assay.
• Assessment of within-run coefficient of variation (CV) and inter-assay correlation (r-values).
• Analysis of assay linearity and identification of proportional biases, particularly at higher concentrations.

Main Results:

• All evaluated C-peptide assays demonstrated good correlation (r = 0.925 to 0.978).
• Significant proportional biases were observed between assays, especially at higher C-peptide concentrations.
• Assay linearity was confirmed up to 4.5 ng/ml, and all methods were easy to perform.

Conclusions:

• Despite good correlation, systematic biases necessitate further standardization of C-peptide assays.
• Laboratories should establish local, method-specific reference ranges for C-peptide measurements.
• Standardization efforts are crucial to ensure reliable and consistent C-peptide quantification in clinical settings.