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Evaluation of Kappa Index as a Tool in the Diagnosis of Multiple Sclerosis: Implementation in Routine Screening
Carmen Teresa Sanz Diaz1, Silvia de Las Heras Flórez1, Mercedes Carretero Perez1
1Clinical Analysis Laboratory, Hospital Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain.
Insights
The kappa index (K-Index) shows high sensitivity for diagnosing multiple sclerosis (MS) by detecting intrathecal immunoglobulin synthesis. This method offers a faster, cost-effective screening tool for MS compared to traditional tests.
Area of Science:
- Neuroimmunology
- Clinical Chemistry
- Diagnostic Biomarkers
Background:
- Multiple sclerosis (MS) is a central nervous system inflammatory demyelinating disease.
- Intrathecal immunoglobulin synthesis is a hallmark of MS, typically detected by oligoclonal bands (OCBs).
- Cerebrospinal fluid (CSF) kappa free light chains (K-FLCs) and the derived kappa index (K-Index) are emerging biomarkers for MS.
Purpose of the Study:
- To evaluate the diagnostic performance of the K-Index for the differential diagnosis of MS in a suspected MS cohort.
- To compare the sensitivity and specificity of the K-Index against OCBs, the current gold standard.
- To propose a cost-effective algorithm for MS screening using K-FLC and K-Index analysis.
Main Methods:
- Quantitative measurement of K-FLCs in parallel serum and CSF samples using turbidimetry.
- Calculation of the K-Index (CSF/serum K-FLC divided by CSF/serum albumin).
- Receiver operating characteristic (ROC) analysis to determine optimal K-Index cutoffs and compare diagnostic performance with OCB testing.
Main Results:
- MS patients exhibited significantly higher K-Index levels compared to non-MS patients (66.96 vs. 0.025, p < 0.0001).
- An optimal K-Index cutoff of 3.045 demonstrated high sensitivity (0.9778) and good specificity (0.8629) for MS screening.
- The K-Index showed higher sensitivity and slightly lower specificity than OCB testing (Sens. 0.8889, Spec. 0.9086).
Conclusions:
- The K-Index is a sensitive and specific biomarker for detecting intrathecal immunoglobulin synthesis in MS.
- The K-Index offers a valuable, rapid, and cost-effective tool for initial MS screening.
- A proposed algorithm integrating K-Index analysis with selective OCB testing can streamline MS diagnosis.
Abstract:
Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. Previous studies have shown that cerebrospinal fluid (CSF) kappa free light chains (K-FLCs) may have a role in MS diagnosis. In this regard, the kappa index (K-Index) has demonstrated higher sensitivity, and slightly lower specificity than oligoclonal bands (OCBs), the gold standard for the detection of intrathecal immunoglobulin synthesis, a feature of MS. Here, we evaluated the performance of the K-Index (K-Index = CSF/serum K-FLC divided by CSF/serum albumin) for the differential diagnosis of MS in a cohort of patients with suspected MS. K-FLCs were quantitatively measured in parallel serum and CSF samples by turbidimetry (Freelite Mx reagent on an Optilite system, The Binding Site Group Ltd). From 160 (63.4%) of a total of 252 patients who had K-FLC in CSF <0.03 mg/dl, below the sensitivity limit of the technique, only one had a diagnosis of MS. However, the absence of OCB in this same patient suggested no synthesis of intrathecal immunoglobulin. Globally, MS patients presented significantly higher K-Index levels than patients without an MS diagnosis (66.96 vs. 0.025, respectively; p < 0.0001). In agreement, patients with positive OCB testing also exhibited higher K-Index levels than patients negative for OCB (65.02 vs. 0.024, respectively; p < 0.0001). An optimal K-Index cutoff of 3.045 was defined by receiver operating characteristic (ROC) analysis for screening suspected MS, achieving a higher diagnostic sensitivity and slightly lower specificity than OCB (Sens. 0.9778 and Spec. 0.8629 vs. Sens. 0.8889 and Spec. 0.9086, respectively). A previously reported K-Index cutoff of 6.6 also showed good diagnostic performance (Sens. 0.9333; Spec. 0.8731), validating its power as a diagnostic biomarker for MS. Finally, a time- and cost-effective algorithm for MS screening is proposed that would offer an initial rapid evaluation of the intrathecal immunoglobulin synthesis through the K-FLC in CSF and K-Index analysis, followed by reflexing OCB testing that may be ordered more selectively.
