Simstich Sebastian, Züllig Thomas, D'Aurizio Federica, Biasotto Alessia, Colao Annamaria, Isidori Andrea M, Lenzi Andrea, Fauler Günter, Köfeler Harald C, Curcio Francesco, Herrmann Markus
Clinical Institute of Medical and Chemical Laboratory Diagnosis, Medical University of Graz, Austria.
Core Facility Mass Spectrometry, Medical University of Graz, Austria; Institute of Molecular Biosciences, University of Graz, Austria.
Clin Biochem. 2023 Apr;114:95-102. doi: 10.1016/j.clinbiochem.2023.02.008. Epub 2023 Feb 26.
Calibration is an important source of variability in liquid chromatography mass spectrometry (LC-MS) methods for insulin-like growth factor 1 (IGF-1). This study investigated the impact of different calibrator matrices on IGF-1 measurements by LC-MS. Moreover, the comparability of immunoassays and LC-MS was assessed.
DESIGN & METHODS: Calibrators from 12.5 to 2009 ng/ml were prepared by spiking WHO international Standard (ID 02/254 NIBSC, UK) into the following matrices: native human plasma, fresh charcoal-treated human plasma (FCTHP), old charcoal-treated human plasma, deionized water, bovine serum albumin (BSA), and rat plasma (RP). A validated in-house LC-MS method was calibrated repeatedly with these calibrators. Then, serum samples from 197 growth hormone excess and deficiency patients were analysed with each calibration.
The seven calibration curves had different slopes leading to markedly different patient results. The largest differences in IGF-1 concentration from the median (interquartile range) was observed with the calibrator in water and the calibrator in RP (336.4 [279.6-417.0] vs. 112.5 [71.2-171.2], p < 0.001). The smallest difference was observed with calibrators in FCTHP and BSA (141.8 [102.0-198.5] vs. 127.9 [86.9-186.0], p < 0.049). Compared to LC-MS with calibrators in FCTHP, immunoassays showed relevant proportional bias (range: -43% to -68%), constant bias (range: 22.84 to 57.29 ng/ml) and pronounced scatter. Comparing the immunoassays with each other revealed proportional bias of up to 24%.
The calibrator matrix is critical for the measurement of IGF-1 by LC-MS. Regardless of the calibrator matrix, LC-MS shows poor agreement with immunoassays. Also, the agreement between different immunoassays is variable.
校准是胰岛素样生长因子1（IGF-1）液相色谱-质谱联用（LC-MS）法中变异性的一个重要来源。本研究调查了不同校准物基质对LC-MS法测定IGF-1的影响。此外，还评估了免疫测定法与LC-MS法的可比性。
通过将世界卫生组织国际标准品（编号02/254，英国国家生物标准与控制研究所）加入以下基质中，制备浓度范围为12.5至2009 ng/ml的校准物：天然人血浆、新鲜活性炭处理的人血浆（FCTHP）、陈旧活性炭处理的人血浆、去离子水、牛血清白蛋白（BSA）和大鼠血浆（RP）。使用这些校准物对经过验证的内部LC-MS方法进行多次校准。然后，对197例生长激素过多和缺乏患者的血清样本进行每种校准下的分析。
七条校准曲线斜率不同，导致患者结果明显不同。在校准物为水和校准物为RP时，观察到IGF-1浓度与中位数（四分位间距）的最大差异（336.4 [279.6 - 417.0] 对比 112.5 [71.2 - 171.2]，p < 0.001）。在校准物为FCTHP和校准物为BSA时观察到的差异最小（141.8 [102.0 - 198.5] 对比 127.9 [86.9 - 186.0]，p < 0.049）。与校准物为FCTHP的LC-MS法相比，免疫测定法显示出显著的比例偏差（范围：-43%至-68%）、恒定偏差（范围：22.84至57.29 ng/ml）和明显的离散度。相互比较免疫测定法发现比例偏差高达24%。
校准物基质对于LC-MS法测定IGF-1至关重要。无论校准物基质如何，LC-MS法与免疫测定法的一致性都较差。此外，不同免疫测定法之间的一致性也存在差异。
