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Test Code KCSF Immunoglobulin Kappa Free Light Chain, Spinal Fluid


Ordering Guidance


For evaluation of multiple sclerosis, Multiple Sclerosis (MS) Profile, Serum and Spinal Fluid, SFIG/ Cerebrospinal Fluid IgG Index Profile, Serum and Spinal Fluid in conjunction with OLIG / Oligoclonal Banding, Serum and Spinal Fluid are still available as individually orderable tests.

 

In addition, a multiple sclerosis profile (MSP3 / Multiple Sclerosis (MS) Profile, Serum and Spinal Fluid) is available. This profile starts with immunoglobulin kappa free light chain testing. When that is borderline or elevated, additional testing for oligoclonal banding will be performed and results interpreted accordingly.



Specimen Required


Specimen Type: Spinal fluid

Container/Tube: Sterile vial

Specimen Volume: 1 mL

Collection Instructions: Label specimen as spinal fluid.


Useful For

Diagnosing multiple sclerosis and other demyelinating conditions

 

Evaluating patients who present with a clinically isolated syndrome in which the patient reports symptoms (headaches, optic neuritis, fatigue, and many others, depending on the disease location) characteristic of inflammation and demyelination of the central nervous system

 

Recommended in cases where the imaging findings are atypical and in populations in which multiple sclerosis is less common (eg, children, older individuals, or non-White populations)

 

The test is not useful when a clear diagnosis is already known because a positive result does not correlate with severity of the disease or disease outcomes.

Method Name

Nephelometry

Reporting Name

Kappa Free Light Chain, CSF

Specimen Type

CSF

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
CSF Frozen (preferred) 28 days
  Refrigerated  72 hours
  Ambient  24 hours

Reject Due To

Gross hemolysis Reject
Gross icterus OK

Clinical Information

Multiple sclerosis (MS) is a chronic demyelinating disease of the central nervous system (CNS). The clinical diagnosis of MS is centered on each patient while applying diagnostic guidelines. Immunoglobulin free light chain (FLC) presence in cerebrospinal fluid (CSF) is an alternative for diagnosing MS using nephelometry. Light chains are produced in excess during antibody formation and secreted from plasma cells or plasma blasts. Quantitative FLC assays use antisera directed against epitopes that are exposed only when the light chains are free (unbound to heavy chain) in solution. FLC immunoassays can be used to specifically quantitate FLC even in the presence of large concentrations of polyclonal immunoglobulins.

 

Routine use of isoelectric focusing electrophoresis coupled with IgG-specific immunoblotting (IgG-IEF) identifies immunoglobulins specific to the CNS. This method is part of the diagnostic criteria used in cases of MS, ie, oligoclonal banding (OLIG / Oligoclonal Banding, Serum and Spinal Fluid). However, oligoclonal banding is a labor-intensive technique that includes subjective interpretation of IgG bands from paired CSF and serum.

 

This test, when considered positive at a concentration greater than or equal to 0.1000 mg/dL as a medical decision point, has a sensitivity of 70.4% with a specificity of 86.8%. The differences between this test and the oligoclonal banding analysis are not statistically significant (p=0.20), and the 2 tests show comparable performance. However, this test does not require a paired serum specimen, offers a shorter turnaround-time for results, and an objective quantitative result.

 

This testing is most useful in patients presenting with a clinically isolated syndrome, which is a clinical episode where patient reports symptoms (headaches, optic neuritis, fatigue, and many others, depending on the disease location) characteristic of inflammation and demyelination of the CNS, and needs to be checked by a neurologist. This is when the likelihood of a diagnosis of MS is greater or most likely but not yet known or confirmed. CSF laboratory testing is also strongly recommended in cases where the imaging findings are atypical and in populations in which MS is less common (eg, children, older individuals, or non-White populations).

Reference Values

Medical Decision Point: 0.1000 mg/dL

Positive: ≥0.1000 mg/dL

Borderline: 0.0600 mg/dL-0.0999 mg/dL

Negative <0.0600 mg/dL

Interpretation

When a result is less than 0.0600 mg/dL, the kappa free light-chain concentration measured in cerebrospinal fluid (CSF) is lower than the threshold associated with demyelinating disease. This is a negative result. Clinical correlation is recommended.

 

When result is between 0.0600 and 0.0999 mg/dL, this is a borderline result. These findings are not specific for multiple sclerosis (MS) because CSF-specific immunoglobulin synthesis may also be detected in patients with other neurologic diseases (infectious, inflammatory, cerebrovascular, autoimmune, and paraneoplastic). If clinically indicated, consider additional CSF testing such as oligoclonal banding by isoelectric focusing and CSF IgG index.

 

When result is greater than or equal to 0.1000 mg/dL, the kappa free light chain concentration measured in CSF is at or greater than the threshold associated with demyelinating disease. This is a positive result. These findings, however, are not specific for MS because CSF-specific immunoglobulin synthesis may also be detected in patients with other neurologic diseases (infectious, inflammatory, cerebrovascular, autoimmune, and paraneoplastic). If clinically indicated, consider additional CSF testing such as oligoclonal banding by isoelectric focusing and CSF IgG index.

 

A Mayo Clinic study published in 2018 with 325 patients suggested that a kappa free light-chain concentration in CSF greater than or equal to 0.06 mg/dL has 92.5% clinical sensitivity in the diagnosis of multiple sclerosis.(1)

 

A second, larger Mayo Clinic study with 1355 patients published in 2021 showed that a kappa CSF concentration greater than or equal to 0.06 mg/dL had approximately 89% sensitivity. When the kappa level was greater than or equal to 0.1 mg/dL, it had similar sensitivity (87%) to the finding of two unique CSF oligoclonal bands (89%).(2)

Day(s) Performed

Monday through Friday

Report Available

1 to 3 days

Specimen Retention Time

14 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

83521

LOINC Code Information

Test ID Test Order Name Order LOINC Value
KCSF Kappa Free Light Chain, CSF 48774-4

 

Result ID Test Result Name Result LOINC Value
KCSF Kappa Free Light Chain, CSF 48774-4