The detection of oligoclonal bands in cerebrospinal fluid (CSF) is an important tool in the diagnostic work-up of multiple sclerosis. These bands are indicators of the local production, within the central nervous system of antibodies of restricted specificities. Until recently, these have been detected by simple electrophoresis of highly concentrated samples of CSF. However this technique requires large amounts of CSF, which are not always available, lacks sensitivity and is now being replaced by isoelectric focusing (IEF) of CSF.

Isoelectric focusing is a highly specialised technique, that separates proteins with great precision, according to their charge (isoelectric point). A small quantity of unconcentrated CSF (or serum) is loaded onto a special gel containing within it, a fixed pH gradient. When subjected to an electric charge, proteins move to their isoelectric point and then move no further. This procedure has been in use in research laboratories for a considerable period of time.  However, technical advances have now made it possible to use this method in the pathology laboratory, where it can be used to accurately fingerprint the clonality of proteins within CSF. Polyclonal immunoglobulins, migrate as a smear, whilst monoclonal, or oligoclonal bands, migrate as a series of discrete bands.   This test is extremely sensitive and specific, especially, when it is coupled with immunoblotting as a means of visualising only immunoglobulins within the gel. 

Due to the greatly improved sensitivity and specificity, and the requirement for only very small amounts of material, effective immediately, CSF EPGs will be replaced by CSF IEF which will include immunoblotting to detect the IgG bands. This methodology is that recommended in Freedman et al. Recommended Standard of Cerebrospinal Fluid Analysis in the Diagnosis of Multiple Sclerosis. A Consensus Statement. Arch Neurol . 2005;62:865-870.

To undertake this test we require 0.5ml amount of CSF and 0.5ml amount of serum. The serum must have been collected within 1 week of the collection of the CSF sample. The serum sample is necessary so that we can ensure that any oligoclonal bands detected are of CSF origin, and do not simply represent spill over into the CSF of oligoclonal or monoclonal bands that have been produced elsewhere and are present in serum.

Examples of the various patterns that can be seen on CSF IEF, are demonstrated below. 

he expected frequency of positive results at levels >20u and >40u in various patient groups is shown in the table below.

Using CSF IEF the detection of oligoclonal bands present within CSF (and absent from serum) are quoted as having sensitivities and specificities for multiple sclerosis of between 85% and 95%.