Ann Lab Med.  2023 Jul;43(4):345-354. 10.3343/alm.2023.43.4.345.

An Accurate Isotope Dilution Liquid Chromatography-Tandem Mass Spectrometry Method for Serum C-Peptide and Its Use in Harmonization in China

• Deng Y
• Zhang C
• Wang J
• Zeng J
• Zhang J
• Zhang T
• Zhao H
• Zhou W
• Zhang C

• KMID: 2551952
• DOI: http://doi.org/10.3343/alm.2023.43.4.345

Abstract

Background
Serum C-peptide results from various routine methods used in China are highly variable, warranting well-performing methods to serve as an accuracy base to improve the harmonization of C-peptide measurements in China. We developed an accurate isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC–MS/MS) method for serum C-peptide measurement and explored its use in harmonization.
Methods
After protein precipitation with ZnSO4 solution, C-peptide was extracted from serum samples by anion-exchange solid-phase extraction and quantified by ID-LC–MS/MS in positive ion mode. The precision and analytical recovery of the ID-LC–MS/MS method were assessed. Seventy-six serum samples were analyzed using the ID-LC–MS/MS method and six routine immunoassays. Ordinary linear regression (OLR) and Bland-Altman (BA) analyses were conducted to evaluate the relationship between the ID-LC–MS/MS method and routine immunoassays. Five serum pool samples assigned using the ID-LC–MS/MS method were used to recalibrate the routine assays. OLR and BA analyses were re-conducted after recalibration.
Results
The within-run, between-run, and total precision for the ID-LC–MS/MS method at four concentrations were 1.0%–2.1%, 0.6%–1.2%, and 1.3%–2.2%, respectively. The analytical recoveries for the ID-LC–MS/MS method at three concentrations were 100.3%–100.7%, 100.4%–101.0%, and 99.6%–100.7%. The developed method and the immunoassays were strongly correlated, with all R2 >0.98. The comparability among the immunoassays was substantially improved after recalibration.
Conclusions
The performance of the ID-LC–MS/MS method was carefully validated, and this method can be used to improve the harmonization of serum C-peptide measurements in China.

Keyword

Serum C-peptide; Liquid chromatography-tandem mass spectrometry; Method comparison; Diabetes mellitus; Harmonization

Figure

• 

  Fig. 1 Representative chromatograms of C-peptide and IS in a serum sample. (A) C-peptide (820.0 pmol/L): m/z 1,007.7 → 147.2, (B) IS (1100.0 pmol/L): m/z 1,011.7 → 147.2.

• 

  Fig. 2 OLR and BA plots of the agreement between the ID-LC–MS/MS method and the six routine immunoassays before recalibration. (A, C, E, G, I, and K) OLR plots for the Roche, Mindray, Snibe, Abbott, Beckman, and Siemens assays, respectively. (B, D, F, H, J, and L) BA plots for the Roche, Mindray, Snibe, Abbott, Beckman, and Siemens assays, respectively. Abbreviations: ID-LC–MS/MS, isotope dilution liquid chromatography–tandem mass; OLR, ordinary linear regression; BA, Bland–Altman.

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