Rej R, Drake P
Wadsworth Center for Laboratories and Research, School of Public Health, State Univ New York, Albany 12201-0509.
Scand J Clin Lab Invest Suppl. 1991;205:47-54. doi: 10.3109/00365519109104601.
Immunoassay systems require calibration protocols that are normally more sophisticated than many analytical techniques in routine clinical use. Calibrators used in such assays may differ significantly from the analyte in clinical specimens. Differences in the properties of calibrators, or reference materials, from those of clinical specimens may include: species origin of the calibrator for an analyte; integrity of the molecular species; matrix of the calibration solution; addition of preservative agents. Owing to the large number of potential differences in the properties of calibrators and those of serum specimens that may affect immunoassay results, the concept of commutability that we originated and first applied to enzyme activity measurements can readily be applied to immunoassay determinations. We specifically examined the properties of calibration materials in nine commercial immunoassay tests for human thyrotropin. Significant non-commutability of materials was demonstrated. The measured results obtained with authentic patient sera differed by a factor of approximately two fold between the techniques exhibiting the lowest and greatest numeric results. Considerably larger intermethod biases were found for calibration materials. Multivariate analysis revealed that the patient sera formed a highly focussed pattern. The calibration materials for one instrument system also focussed in this group. Other calibrators formed three foci indicating similar patterns of commutability within each of the three groups. Clustering was independent of the amount of thyrotropin in the patient specimens, but appeared to be concentration-dependent for at least some of the calibrators. Thus the availability of a common calibration material appears feasible, but not presently available in many commercial products. A processed human serum, a candidate material for use in our proficiency testing program, was projected in the same cluster as authentic patient sera indicating that this material has intermethod properties identical to patient sera (i.e. fully commutable).
免疫分析系统需要的校准方案通常比常规临床使用的许多分析技术更为复杂。此类分析中使用的校准物可能与临床标本中的分析物有显著差异。校准物或参考物质与临床标本在性质上的差异可能包括：分析物校准物的物种来源；分子物种的完整性；校准溶液的基质；防腐剂的添加。由于校准物和血清标本在性质上存在大量可能影响免疫分析结果的潜在差异，我们首创并首次应用于酶活性测量的互换性概念可很容易地应用于免疫分析测定。我们专门检测了九种用于人促甲状腺激素的商业免疫分析测试中校准材料的特性。结果表明材料存在显著的不可互换性。用真实患者血清获得的测量结果在数值最低和最高的技术之间相差约两倍。在校准材料方面发现了更大的方法间偏差。多变量分析显示患者血清形成了高度集中的模式。一个仪器系统的校准材料也集中在这一组中。其他校准物形成了三个焦点，表明三组中每组内部具有相似的互换性模式。聚类与患者标本中促甲状腺激素的含量无关，但至少对某些校准物而言似乎与浓度有关。因此，使用通用校准材料似乎是可行的，但目前在许多商业产品中尚未实现。一种经过处理的人血清，作为我们能力验证计划中使用的候选材料，与真实患者血清被归为同一类，这表明该材料具有与患者血清相同的方法间特性（即完全可互换）。
