Institute of Clinical Chemistry, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland.
Clin Chem Lab Med. 2011 Jul;49(7):1217-9. doi: 10.1515/CCLM.2011.189. Epub 2011 May 17.
Serum protein electrophoresis is used as a screening test for monoclonal gammopathies. Here, we present a case of a high-concentration monoclonal immunoglobulin (M-protein) that was missed by serum protein electrophoresis on a Capillarys 2 capillary zone electrophoresis system. The aim of our study was to identify the reason for the failure of the system to detect the M-protein.
M-protein solubility was examined in response to temperature, pH, ionic strength, the chaotropic agent urea and the reducing agent 2-mercaptoethanol.
Precipitation of the M-protein was not cold-induced, but solubility decreased at pH 8.5 or higher, when the pH approached the apparent isoelectric point. The M-protein also precipitated in alkaline Capillarys 2 electrophoresis buffer (pH 10), which was the reason for the false-negative electrophoresis result. Precipitation of the M-protein was not related to the ionic strength of the buffer. Solubility improved in presence of urea. Pre-treatment of serum with 2-mercaptoethanol revealed the missing M-protein peak of 36 g/L on the electropherogram.
This case shows that insolubility of M-proteins in alkaline buffer is one possible cause of false-negative results on capillary zone electrophoresis systems. False-negative results should be considered, especially when accompanying laboratory results are inconsistent with the electropherogram.
血清蛋白电泳用于单克隆丙种球蛋白病的筛查试验。在此，我们报告了一例在 Capillarys 2 毛细管区带电泳系统上血清蛋白电泳未能检测到高浓度单克隆免疫球蛋白 (M 蛋白) 的病例。我们的研究目的是确定该系统未能检测到 M 蛋白的原因。
检测 M 蛋白对温度、pH 值、离子强度、变性剂脲和还原剂 2-巯基乙醇的溶解度。
M 蛋白的沉淀不是冷诱导的，但在 pH 值为 8.5 或更高时，接近等电点时，溶解度降低。M 蛋白也在碱性 Capillarys 2 电泳缓冲液（pH 10）中沉淀，这是电泳结果假阴性的原因。M 蛋白的沉淀与缓冲液的离子强度无关。在存在脲的情况下，溶解度增加。用 2-巯基乙醇预处理血清后，电泳图谱上出现了缺失的 36 g/L 的 M 蛋白峰。
本病例表明，M 蛋白在碱性缓冲液中的不溶性是毛细管区带电泳系统出现假阴性结果的一个可能原因。应考虑假阴性结果，特别是当伴随的实验室结果与电泳图谱不一致时。
