Data from: Assessment of intrathecal free light chain synthesis: comparison of different quantitative methods with the detection of oligoclonal free light chains by isoelectric focusing and affinity-mediated immunoblotting

Objectives: We aimed to compare various methods for free light chain (fLC)
quantitation in cerebrospinal fluid (CSF) and serum and to determine
whether quantitative CSF measurements could reliably predict intrathecal
fLC synthesis. In addition, we wished to determine the relationship
between free kappa and free lambda light chain concentrations in CSF and
serum in various disease groups. Methods: We analysed 166 paired CSF and
serum samples by at least one of the following methods: turbidimetry
(Freelite™, SPAPLUS), nephelometry (N Latex FLC™, BN ProSpec), and two
different (commercially available and in-house developed) sandwich ELISAs.
The results were compared with oligoclonal fLC detected by
affinity-mediated immunoblotting after isoelectric focusing. Results:
Although the correlations between quantitative methods were good, both
proportional and systematic differences were discerned. However, no major
differences were observed in the prediction of positive oligoclonal fLC
test. Surprisingly, CSF free kappa/free lambda light chain ratios were
lower than those in serum in about 75% of samples with negative
oligoclonal fLC test. In about a half of patients with multiple sclerosis
and clinically isolated syndrome, profoundly increased free kappa/free
lambda light chain ratios were found in the CSF. Conclusions: Our results
show that using appropriate method-specific cut-offs, different methods of
CSF fLC quantitation can be used for the prediction of intrathecal fLC
synthesis. The reason for unexpectedly low free kappa/free lambda light
chain ratios in normal CSFs remains to be elucidated. Whereas CSF free
kappa light chain concentration is increased in most patients with
multiple sclerosis and clinically isolated syndrome, CSF free lambda light
chain values show large interindividual variability in these patients and
should be investigated further for possible immunopathological and
prognostic significance.