Combined use of Kappa Free Light Chain Index and Isoelectrofocusing of Cerebro-Spinal Fluid in Diagnosing Multiple Sclerosis: Performances and Costs.

BACKGROUND: Isoelectrofocusing (IEF) to detect oligoclonal bands (OBCs) in cerebrospinal fluid (CSF) is the gold standard approach for evaluating intrathecal immunoglobulin synthesis in multiple sclerosis (MS) but the kappa free light chain index (KFLCi) is emerging as an alternative marker, and the combined/sequential uses of IEF and KFLCi have never been challenged. METHODS: CSF and serum albumin, IgG, kFLC and lFLC were measured by nephelometry; albumin, IgG and kFLC quotients as well as Link and kFLC indexes were calculated; OCBs were evaluated by immunofixation. A total of 150 consecutive patients: 48 with MS, 32 with other neurological inflammatory diseases (NID), 62 with neurological non-inflammatory diseases (NNID), and 8 without any detectable neurological disease (NND) were investigated. RESULTS: Both IEF and KFLCi showed a similar accuracy as diagnostic tests for multiple sclerosis. The high sensitivity and specificity associated with the lower cost of KFLCi suggested to use this test first, followed by IEF as a confirmative procedure. The sequential use of IEF and KFLCi showed high diagnostic efficiency with cost reduction of 43 and 21%, if compared to the contemporary use of both tests, or the unique use of IEF in all patients. CONCLUSIONS: The "sequential testing" using KFLCi followed by IEF in MS represents an optimal procedure with accurate performance and lower costs.

Hemolysis is a major cause of variability in insulin measurement during oral glucose tolerance test in children.

BACKGROUND: The oral glucose tolerance test (OGTT) is widely employed to evaluate insulin resistance in children with growth hormone deficiency. Due to the difficulty in blood sampling, hemolysis is a frequent pre-analytic interference. The present study was performed to characterize the effects of hemolysis on insulin assays, in order to assess the need to generate automatic hemolysis reports and/or to reject hemolyzed samples. METHODS: Insulin plasma levels were measured using a Siemens ADVIA Centaur on samples obtained from children with suspected GH deficiency at risk for insulin resistance during OGTT. RESULTS: The presence of hemolysis (with a concentration of free hemoglobin above 75 mg/dL) promotes a dose- and time-dependent decrease in immunoreactive insulin at any time-point evaluated during OGTT. As a consequence, the variability of insulin is particularly high (often exceeding 100% of the mean value) as compared to that of glucose. This variability is markedly reduced after removal of the hemolyzed samples. CONCLUSIONS: When hemolysis is not taken into account a misinterpretation of insulin secretion pattern can occur. It is therefore imperative to: (i) analyze blood samples immediately after sampling, (ii) reject samples with a concentration of free hemoglobin equal to or above 125 mg/dL and (iii) always report the possible interference.

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

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 positiveimmunoglobulin G (IgG) index when testing for oligoclonal bands (OB) is negative or not performed". Theaim of this study was to compare the performance of K and IgG indexes for MS diagnosis and OB detectionin 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, IgGand free light chains were measured by nephelometry and used to calculate IgG and K indexes. Althoughthe two markers were highly related (r = 0.75, r2 = 0.55, p < 0.0001), the K index showed greater sensitivity andnegative predictive value (versus the IgG index) for OB detection (97% versus 48% and 97% versus 71%) andMS diagnosis (96% versus 50% and 98% versus 78%). These results support K index (and not IgG index) as afirst-line marker for MS, followed by IEF, according to a sequential testing approach in CSF analysis.