If the sFLC concentration is many thousands of mg/L why is there no band on SPE?
The sensitivity of SPE for monoclonal bands depends upon the width of the band and its position in the gel in relation to other plasma proteins. Narrow monoclonal bands in the gamma region in association with hypogammaglobulinaemia will be visible at 200-400mg/L. The same band in a beta position, perhaps superimposed on transferrin, will be invisible. The monoclonal protein may need to be over 2,000mg/L to be visible in this area of the gel. In addition, monoclonal FLCs may be polymerised to different extents and then they migrate on electrophoresis gels as diffuse bands. This is frequently found in NSMM and is well-documented in LCMM. In these patients, even 5,000mg/L of monoclonal protein may be difficult to detect above the background of the other plasma proteins.
