Background The detection of the Epstein–Barr capsid antigen (VCA) immunoglobulin A (IgA) is widely used in the diagnosis of nasopharyngeal carcinoma (NPC), but a reference standard for evaluating the presence of VCA-IgA is not yet available. Therefore, a reference standard is urgently needed for a uniform and quantitative detection of VCA-IgA. Methods A mixed reference serum from three NPC patients diluted with healthy subject serum was made as a potential first international standard for VCA-IgA. VCA-IgA was detected in twenty NPC patients by four ELISA kits and two chemiluminescent immunoassays kits using the reference as a calibration curve. The performance of these six kits was evaluated, and the quantitative results were compared. Results Our results showed a good linearity of the reference in different kits. Without reference, the difference of the total coefficient of variation (from 3.98 to 43.11%) and Within-run coefficient of variation (from 2.47 to 19.66%) was large in the 6 kits. The positive and negative coincidence rate between the 6 kits and indirect immunofluorescence for NPC diagnosis was 75% overall agreement, but a difference among the six kits was found, ranging from 55 to 90%. The concentration of VCA-IgA in the 20 NPC samples led in the division into three categories such as negative, low, or medium/high positive, but these concentrations were significantly different within these three categories depending on the kit used of the 6 considered. However,a good correlation (R 2 = 0.986) was observed between Antu and Beier ELISA kits. Conclusions The reference serum mightbe used as a reference standard for a better comparison of the results from different kits/laboratories. However, the quantitative results of some kits are still inconsistent due to the diversity of VCA antigens.

中文翻译：

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Epstein-Barr病毒衣壳抗原免疫球蛋白A候选国际参考文献的初步评价

背景 爱泼斯坦-巴尔衣壳抗原 (VCA) 免疫球蛋白 A (IgA) 的检测广泛用于鼻咽癌 (NPC) 的诊断，但尚无评估 VCA-IgA 存在的参考标准。因此，迫切需要一个参考标准来统一和定量检测 VCA-IgA。方法 用健康受试者血清稀释三名鼻咽癌患者的混合参考血清作为 VCA-IgA 潜在的第一个国际标准。使用参考作为校准曲线，通过四种 ELISA 试剂盒和两种化学发光免疫测定试剂盒在 20 名 NPC 患者中检测到 VCA-IgA。对这六种试剂盒的性能进行了评估，并对定量结果进行了比较。结果 我们的结果显示不同试剂盒中的参考具有良好的线性。没有参考，6个试剂盒的总变异系数（从3.98到43.11%）和批内变异系数（从2.47到19.66%）的差异很大。6个试剂盒与间接免疫荧光诊断鼻咽癌的阳性和阴性符合率为75%，但6个试剂盒之间存在差异，范围为55%~90%。20 份 NPC 样本中 VCA-IgA 的浓度导致分为三类，例如阴性、低或中/高阳性，但根据所考虑的 6 种使用的试剂盒，这三类中的浓度存在显着差异。然而，在安图和贝尔ELISA试剂盒之间观察到良好的相关性（R 2 = 0.986）。结论参考血清可作为参考标准，更好地比较不同试剂盒/实验室的结果。但由于 VCA 抗原的多样性，部分试剂盒的定量结果仍不一致。