Discrepancies between qualitative and quantitative analysis of cerebrospinal fluid IgG: densitometric comparison of nephelometry-silver versus immuno-enzymes

BACKGROUND: Detection of local synthesis of IgG within the central nervous system is important for the diagnosis of brain inflammatory diseases such as multiple sclerosis. This is typically done by comparing the amounts of IgG in serum and parallel cerebrospinal fluid (CSF). Although there have been well-described problems with qualitative versus quantitative measurements of abnormal IgG, such as in myeloma paraproteins, similar difficulties are also found with CSF IgG. METHODS: Traditional quantitative analysis of IgG by rate nephelometry was followed by separation of the IgG using isoelectric focusing and then either silver stain or immunofixation. Finally, quantitative analysis was performed by scanning densitometry using public domain software downloaded from the National Institutes of Health. RESULTS: We report here the major discrepancies that can occur with CSF IgG between the silver stain versus the IgG stain. CONCLUSIONS: We concur with the earlier recommendation that qualitative separation followed by densitometric estimation of enzyme-linked immunofixation is also more useful than simple quantitative nephelometric analysis followed by silver staining in the detection of local synthesis of IgG, analogous to the earlier work on paraproteins.