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J. Clin. Med. 2019, 8(4), 446; https://doi.org/10.3390/jcm8040446

K Index is a Reliable Marker of Intrathecal Synthesis, and an Alternative to IgG Index in Multiple Sclerosis Diagnostic Work-Up

1
Laboratory of Clinical Biochemistry, Department of Health Sciences, AOU Maggiore della Carità, University of Piemonte Orientale, corso Mazzini 18, 28100 Novara, Italy
2
Department of Transational Medicine, Institute of Neurology, AOU Maggiore della Carità, University of Piemonte Orientale, corso Mazzini 18, 28100 Novara, Italy
3
Interdisciplinary Research Center of Autoimmune Diseases (IRCAD), Department of Health Sciences, University of Piemonte Orientale, 28100 Novara, Italy
*
Author to whom correspondence should be addressed.
Received: 14 February 2019 / Revised: 14 March 2019 / Accepted: 29 March 2019 / Published: 2 April 2019
(This article belongs to the Section Neuroscience)
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Abstract

The K free light chain (K) index has been suggested as a reliable marker of intrathecal synthesis, despite the 2017 McDonald criteria for multiple sclerosis (MS) suggesting to “interpret with caution positive immunoglobulin G (IgG) index when testing for oligoclonal bands (OB) is negative or not performed”. The aim of this study was to compare the performance of K and IgG indexes for MS diagnosis and OB detection in a cohort of Italian patients. We enrolled 385 patients (127 MS, 258 non-MS) who had cerebrospinal fluid (CSF) analysis, including isoelectric focusing (IEF), to detect OB in the diagnostic work-up. Albumin, IgG and free light chains were measured by nephelometry and used to calculate IgG and K indexes. Although the two markers were highly related (r = 0.75, r2 = 0.55, p < 0.0001), the K index showed greater sensitivity and negative predictive value (versus the IgG index) for OB detection (97% versus 48% and 97% versus 71%) and MS diagnosis (96% versus 50% and 98% versus 78%). These results support K index (and not IgG index) as a first-line marker for MS, followed by IEF, according to a sequential testing approach in CSF analysis. View Full-Text
Keywords: cerebrospinal fluid; diagnosis; immunoglobulins cerebrospinal fluid; diagnosis; immunoglobulins
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Crespi, I.; Vecchio, D.; Serino, R.; Saliva, E.; Virgilio, E.; Sulas, M.G.; Bellomo, G.; Dianzani, U.; Cantello, R.; Comi, C. K Index is a Reliable Marker of Intrathecal Synthesis, and an Alternative to IgG Index in Multiple Sclerosis Diagnostic Work-Up. J. Clin. Med. 2019, 8, 446.

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