Cabaleiro Diego Rodríguez, Stöckl Dietmar, Kaufman Jean M, Fiers Tom, Thienpont Linda M
Laboratory for Analytical Chemistry, Faculty of Pharmaceutical Sciences, Ghent University, Gent, Belgium.
Clin Chem. 2006 Jun;52(6):1193-6. doi: 10.1373/clinchem.2005.062505. Epub 2006 Apr 13.
Serum C-peptide concentrations reflect pancreatic function in different clinical and diagnostic settings; however, the utility of C-peptide testing is limited by the lack of standardized commercial immunoassays. Standardization can best be done by split-sample comparison with a hierarchically higher reference measurement procedure with a set of native sera. For serum peptides, isotope-dilution liquid chromatography-mass spectrometry (ID-LC/MS) is recommended as a reference measurement procedure.
We evaluated the analytical performance characteristics of an ID-LC/tandem MS procedure for measurement of serum C-peptide after a 2-step solid-phase extraction. To investigate the feasibility of this procedure for use in standardization, we also performed a method comparison with 3 representative commercial assays.
The ID-LC/tandem MS procedure showed maximum within-run, between-run, and total CVs on dedicated sera (C-peptide concentrations, 1.6 and 4.0 mug/L) of 2.1%, 2.5%, and 2.9%, respectively; an accuracy of 94.6%-104.1%; a minimum trueness of 98.1% (95% confidence interval, 96.2%-100.0%), and limits of quantification and detection of 0.15 and 0.03 mug/L, respectively. Deming linear regression analysis of the method-comparison data showed that the immunoassays correlated well with ID-MS and were specific, but lacked intercomparability and trueness. We propose that the deficiencies can be resolved by recalibration on the basis of the method comparison.
The ID-LC/tandem MS procedure is suitable for specific and accurate measurement of basal and stimulated serum concentrations of proinsulin C-peptide fragment 33-63 and is suitable for use in standardization of C-peptide immunoassays.
血清C肽浓度在不同临床和诊断环境中反映胰腺功能；然而，C肽检测的实用性受到缺乏标准化商业免疫测定法的限制。标准化最好通过与一组天然血清的层次更高的参考测量程序进行分样比较来完成。对于血清肽，推荐使用同位素稀释液相色谱-质谱联用（ID-LC/MS）作为参考测量程序。
我们评估了两步固相萃取后用于测量血清C肽的ID-LC/串联质谱法的分析性能特征。为了研究该程序用于标准化的可行性，我们还与3种代表性商业检测方法进行了方法比较。
ID-LC/串联质谱法在专用血清（C肽浓度为1.6和4.0μg/L）上的批内、批间和总变异系数分别为2.1%、2.5%和2.9%；准确度为94.6%-104.1%；最小真实性为98.1%（95%置信区间，96.2%-100.0%），定量限和检测限分别为0.15和0.03μg/L。方法比较数据的Deming线性回归分析表明，免疫测定法与ID-MS相关性良好且具有特异性，但缺乏可比性和真实性。我们建议通过基于方法比较的重新校准来解决这些不足。
ID-LC/串联质谱法适用于特异性和准确地测量胰岛素原C肽片段33-63的基础和刺激血清浓度，适用于C肽免疫测定法的标准化。
