title: Monoclonal gammopathy missed by capillary zone electrophoresis.
abstract: BACKGROUND
  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.
  
  
  METHODS
  M-protein solubility was examined in response to temperature, pH, ionic strength, the chaotropic agent urea and the reducing agent 2-mercaptoethanol.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institute of Clinical Chemistry, Inselspital, Bern University Hospital, and University of Bern, Bern, Switzerland. christof.schild@insel.ch
authors.forename: Christof
authors.initials: C
authors.lastname: Schild
authors.forename: Florence
authors.initials: F
authors.lastname: Egger
authors.forename: Alain
authors.initials: A
authors.lastname: Kaelin-Lang
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Nuoffer
mesh_terms: D019075:Electrophoresis, Capillary / Q000379:methods*; D005188:False Negative Reactions; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007075:Immunoglobulin M / Q000097:blood / Q000737:chemistry; D008623:Mercaptoethanol / Q000494:pharmacology / Q000627:therapeutic use; D010265:Paraproteinemias / Q000097:blood / Q000175:diagnosis* / Q000188:drug therapy; D012995:Solubility
chemical_list: D007075:Immunoglobulin M; D008623:Mercaptoethanol