Intrathecal immunoglobulin synthesis. Comparison of various formulae with the 'gold standard' of isoelectric focusing.

The recent introduction of a further new formula for calculating intrathecal Ig synthesis led us to compare the results of calculations obtained when using it and certain other older formulae with those of isoelectric focusing (IEF), since only the latter proves the intrathecal synthesis of oligoclonal proteins. On comparison, it was found that the results produced by the usual formulae were, without exception, inferior to those of isoelectric focusing. By using Receiver Operating Characteristic (ROC) curves, it is shown that calculations with the Reiber formula agree best with IEF. Virtually the same results are obtained with the "ln IgG index + 1" and "IgG index".

The HAF enigma: origin and clinical consequences of the appearance of high alkaline fractions on isoelectric focusing patterns of cerebrospinal fluid.

High alkaline fractions (HAF) are irregularly present on isoelectric focusing (IEF) patterns of cerebrospinal fluid (CSF). Therefore, this phenomenon was studied retrospectively in more detail. First, the appearance of HAF in time was recorded and attempts were made to discover a relationship to the biochemical parameters of CSF. No such relationship could be established, nor could any effect of age or sex of the patients or any correlation with ambient temperature or clinical diagnosis be shown. Finally, we have shown conclusively that the cause of this random appearance of HAF can be found in the collodion bags used to concentrate the CSF. This irregular feature of the collodion bags also produces a rise in the frequency of appearance of oligoclonal bands on IEF, probably by blocking the passage of proteins. We conclude that the CSF contains protein material, and that the passage of this through the collodion filters during CSF concentration depends on the regularity of composition of the filters used, occasioning the presence (or absence) of a HAF. Of even greater consequence is the observation that when HAFs do not pass a certain collodion filter, other protein-like material can also be retained, leading to the appearance of oligoclonal bands in IEF, and causing more frequent occurrence of IEF patterns containing oligoclonal bands in CSF. Also, a slight change in the spectrum of oligoclonal bands of CSF has been found when HAFs occur. This indicates that the collodion bags do not retain all protein material in the same way.

Intrathecal Ig synthesis. Its detection by isoelectric focusing and IgG index.

In a retrospective study on 999 patients, the likelihood ratios of the IgG index, Tourtellotte formula and IgG concentration in CSF and in serum, the albumin concentration in CSF and in serum, and the total protein in CSF, were compared in predicting intrathecal Ig synthesis. This synthesis was detected with isoelectric focusing (IEF). No patient was included more than once in the data collection. All patients with high IgG and other abnormalities in serum, as well as all xanthochromic and blood-tinged CSF specimens, were excluded from the study. Construction of ROC curves established that the IgG index, Tourtellotte formula and CSF IgG yield the same information: these parameters indicate the presence of intrathecal IgG synthesis. The likelihood ratio for the IgG index at a cut-off point of 0.80 for a positive test is 20; at a cut-off point of 0.5 for a negative test it is 5. For the Tourtellotte formula, it was found that the likelihood ratio reached a maximal value of 7 at a cut-off value of synthesis of 10 mg/day for a positive test. For a negative result, the formula had a likelihood ratio of 6 at a cut-off value of -5. For CSF IgG, it was found that the likelihood ratio was 4 for a positive test with a cut-off value of 0.1 g/l. For a negative outcome, the determination of CSF IgG is only meaningful at a very low cut-off value (0.03 g/l). The other parameters studied (serum IgG concentration, albumin concentration in CSF and in serum, and total protein in CSF) showed a likelihood ratio equal to 1. It is concluded that only the IgG index, the Tourtellotte formula and the CSF IgG concentration have predictive value for intrathecal Ig synthesis as recorded with IEF.