Kappa Free Light Chains, CSF

Last Literature Review: June 2026 Last Update:

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.

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

Results

Results reflect CSF-specific immunoglobulin synthesis.

Kappa Free Light Chains
ResultValueAdditional Information
Negative<0.33 mg/LNot suggestive of intrathecal inflammation; oligoclonal banding is not indicated
Equivocal0.33 mg/L–1.09 mg/LMay be consistent with intrathecal inflammation; consider additional CSF testing (e.g., Oligoclonal Band Profile 0080440)
Positive>1.09 mg/LConsistent with intrathecal inflammation; consider additional CSF testing (e.g., Oligoclonal Band Profile 0080440)

Limitations

kFLCs are not specific to MS and may be elevated in other neurologic conditions, including autoimmune, infectious, inflammatory, cerebrovascular, and paraneoplastic disorders. Additional CSF testing (e.g., oligoclonal banding) may be warranted based on the clinical context.

Related Tests

This test measures CSF kFLCs only. ARUP also offers CSF Kappa Free Light Chains With Reflex to Oligoclonal Banding (3021031) and Oligoclonal Band Profile (0080440).

References