Connect Sign In
FeedbackQuantitative Immunoturbidimetry / Qualitative Isoelectric Focusing
Kappa free light chains (kFLCs) in cerebrospinal fluid (CSF) are used in the diagnostic evaluation of multiple sclerosis (MS) as markers of intrathecal immunoglobulin synthesis. Excess light chains are produced during inflammatory activity in the central nervous system (CNS).
The 2024 McDonald criteria recognize kFLCs as an acceptable alternative to oligoclonal bands (OCBs) for establishing a positive CSF result. Compared with OCB testing, kFLC measurement is faster, less labor-intensive, and more objective.
This test measures CSF kFLCs and, if results are equivocal or positive, automatically reflexes to oligoclonal banding. Reflex testing from positive or equivocal kFLCs to OCBs improves diagnostic accuracy while reducing costs and turnaround times in cases that screen negative. For the most accurate result interpretation, it is recommended to collect CSF and serum specimens on the same day.
Disease Overview
MS is a chronic immune-mediated disease of the CNS characterized by inflammation and demyelination. Diagnosis is based on the McDonald criteria, which incorporate clinical findings, imaging, and laboratory evidence of intrathecal inflammation.
Indications for Use
This test is used to evaluate patients with suspected MS.
Test Interpretation
Reflex Pattern
If kFLCs are equivocal or positive, this test automatically reflexes to oligoclonal banding.
Results
CSF Kappa Free Light Chains
| Result | Value | Additional Information |
|---|---|---|
| Negative | <0.33 mg/L | Not suggestive of intrathecal inflammation; oligoclonal banding is not indicated |
| Equivocal | 0.33 mg/L–1.09 mg/L | May be consistent with intrathecal inflammation; reflex to OCBs performed |
| Positive | >1.09 mg/L | Consistent with intrathecal inflammation; reflex to OCBs performed |
Reflex Oligoclonal Bands
The report includes an OCB number and CSF results. When present, the number of CSF-restricted OCBs is reported. Matched OCBs may also be identified in both serum and CSF.
| Result | OCB Number, CSF | Interpretation |
|---|---|---|
| Negative | 0-1 bands | No OCBs detected in CSF No evidence of intrathecal IgG synthesis |
| Positive | ≥2 CSF-restricted bands | Consistent with intrathecal synthesis of IgG |
| Positive with matched bands | ≥2 CSF-restricted bands and matched bands in CSF and serum | Consistent with intrathecal IgG synthesis Matched serum and CSF bands are consistent with a systemic inflammatory process |
| IgG, immunoglobulin G | ||
Limitations
- Neither kFLCs or OCBs are specific to MS and may be elevated in other neurologic conditions, including autoimmune, infectious, inflammatory, cerebrovascular, and paraneoplastic disorders.
- Approximately 5% of patients with MS have negative OCB results.
- Testing serum and CSF specimens collected on different days may reduce accuracy of OCB results.
Results should be interpreted within the appropriate clinical context.
Related Tests
ARUP also offers standalone tests: Kappa Free Light Chains, CSF (3020898) and Oligoclonal Band Profile (0080440).
References
-
40975101
Montalban X, Lebrun-Frénay C, Oh J, et al. Diagnosis of multiple sclerosis: 2024 revisions of the McDonald criteria. Lancet Neurol. 2025;24(10):850-865.