Application of κ free light chains in cerebrospinal fluid as a biomarker in multiple sclerosis diagnosis: development of a diagnosis algorithm.

BACKGROUND: The determination of κ free light chains (KFLC) in cerebrospinal fluid (CSF) by nephelometry is a feasible alternative to immunoglobulin G oligoclonal bands (OCB) in the evaluation of intrathecal synthesis of immunoglobulin in multiple sclerosis (MS) and other demyelinating diseases. The aim of this study was to assess the diagnostic value of KFLC and its inclusion in a procedure algorithm along with OCB interpretation. METHODS: A cross-sectional study, which included 123 patients with a CSF OCB request, was carried out. Isoelectric focusing followed by immunofixation was used to detect OCB, and nephelometry was used to analyze KFLC. The KFLC index was calculated using CSF/serum quotient of KFLC and albumin. The KFLC index was compared with MS diagnosis to find the optimal cutoff. It was obtained from the receiver operating characteristic (ROC) curves and the Youden method. RESULTS: The CSF KFLC median was 1.66 mg/L in the MS group, whereas in other central nervous system diseases, KFLC showed generally no or only moderate increase in CSF (median 0.10 mg/L). KFLC index showed a significant difference between groups. ROC analysis for CSF KFLC concentration, and KFLC indexes were 91.88% and 93.94%, respectively. The best cutoff for the KFLC index was 2.91 for MS diagnosis (sensitivity: 83.78%; specificity: 85.88%). The proposed algorithm showed high sensitivity (89.19%) and specificity (84.71%). CONCLUSIONS: KFLC determination is rapid and automatized, but it has no higher sensitivity and specificity than OCB in MS diagnosis. Nevertheless, when used in screening, it could reduce the number of manual OCB tests.

Association between seasonal serum folate levels and ultraviolet radiation.

UV radiation has been consistently reported to cause folate photodegradation in vitro and in human skin. Seasonal variations in UV radiation might explain seasonal changes in folate levels in blood. Yet, few studies have addressed this phenomenon. The main objective of this study was to investigate whether a relationship exists between seasonal variations in serum folate levels in a population of Spain (Latitude: 36° 41' 6.88″; Longitude: 4° 30' 0.64″) and the annual variations of solar ultraviolet reached in the localization. From a sample of 118,831 serum folate determinations, two studies were performed. The first one, which included all subjects, showed a decreased in mean folate concentrations in all seasons with respect to winter with lower values in summer. The risk of folate deficiency was 1.37 times greater in summer than in winter (95%CI: 1.29-1.46). In the second study, subjects with a first folate determination in winter and a second one in summer were 3.32 more likely to develop folate deficiency than those with a first folate determination in summer and a second one in winter (95%CI: 1.55 to 7.11). Folate levels showed a seasonal variation inversely related to solar total UV radiation reached in our location, with maximum daily doses of 5000 J m-2 reached in June. A gradual increase in percentage of folate deficiency is observed since spring. So, patients with folate levels close to deficiency are at a higher risk of having folate deficiency in summer.