Clinical Use of κ Free Light Chains Index as a Screening Test for Multiple Sclerosis

Luisa Agnello, PhD; Bruna Lo Sasso, PhD; Giuseppe Salemi, MD; Patrizia Altavilla, BS; Emanuela Maria Pappalardo, BS; Rosalia Caldarella, BS; Francesco Meli, BS; Concetta Scazzone, BS; Giulia Bivona, MD; Marcello Ciaccio, MD, PhD

Disclosures

Lab Med. 2020;51(4):402-407. 

In This Article

Materials and Methods

Patients

Unselected consecutive patients suspected of having MS, who underwent lumbar puncture in their diagnostic work-up for OCB analysis, were enrolled in this study at the Department of Neurology, University Hospital Policlinico P. Giaccone of Palermo, Italy. Blood and CSF specimens were obtained for each patient at enrollment. After routine analysis, all specimens were frozen at −80°C until κFLC analysis. The stability of κFLC measurement after freeze-thaw cycles was tested by Gurtner et al.[14] The authors reported that[14] κFLC can withstand a maximum of 2 freeze/thaw cycles.

The diagnosis of MS was made by an experienced neurologist based on complete medical history, physical examination, CSF analysis (OCB), and MRI findings, according to modified McDonald criteria.[8] No treatment with drugs affecting the immune system was recorded for any patients included in the study; all patients had no comorbidity. The study was approved by the local Ethic Committee, and all patients signed an informed consent.

Biochemical Analysis

Paired CSF and serum specimens were collected by nontraumatic lumbar puncture and venous blood sampling, respectively. Serum and CSF albumin levels were measured by turbidimetric assay using the Optilite Analyser System according to manufacturer (The Binding Site Group Ltd).

OCBs were detected by isoelectric focusing, followed by immunofixation on the semiautomated agarose electrophoresis system Hydrasys (Sebia). The OCB findings were classified as negative or positive according to the conventional criterion of 2 or more CSF-restricted OCB for positivity.

CSF and serum FLC were analysed by turbidimetric assay (Freelite, The Binding Site Group Ltd) on the Optilite Analyser System (The Binding Site Group Ltd), according to the manufacturer. We calculated the CSF/serum ratio of albumin, κFLC, and determined the κFLC index as follows: (CSF κFLC/Serum κFLC)/(CSF Alb/Serum Alb).

Statistical Analysis

The normality of the distributions for each variable was assessed using the Shapiro-Wilk test. Variables were presented as mean (SD) or as median (interquartile range [IQR]) for non-normally distributed continuous variables, and as a percentage for categorical variables.

Comparisons between groups were evaluated by the Mann-Whitney test or Student's t-test, when appropriate. Differences between groups were evaluated using χ2 testing for categorial variables. The clinical usefulness of κFLCi was investigated performing receiver operating characteristic (ROC) curve analysis. The best cutoff value was selected on the basis of the equilibrium between sensitivity and specificity.

The statistical significance of P <.05 was accepted for all tests. Statistical analysis was performed using MedCalc software, version 17.9.2 (MedCalc Software bv).

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